feat(podcasts): played/unplayed queue, background generation, share-sheet audio

Turns the Podcasts tab into a proper podcast-app experience across three
features that compose on a shared background-generation service.

Background generation (#2)
- New PodcastGenerationManager runs generate→poll→download off the player,
  so producing a new episode never stops current playback.
- Headphone taps never interrupt: idle → generate-and-play in the foreground
  (unchanged); already playing → generate in the background, episode lands in
  the library. A "Generating…" banner surfaces active jobs.

Played/unplayed + queue (#1)
- PodcastEntry gains playedAt (old index.json decodes as unplayed).
- Podcasts tab splits into Up Next / Played with a Play All queue that
  auto-advances; finishing marks played; swipe to toggle played state.

Share-extension audio (#3)
- "Create podcast" toggle on the save card, plus configurable Auto-Podcast
  Tags in Settings. The extension enqueues a request into the App Group; the
  main app drains it on launch/foreground and generates in the background.

Closes #1
Closes #2
Closes #3

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Marks.xcodeproj/project.pbxproj

@@ -20,11 +20,13 @@
 		457FCE503CCA82C5F27C6C90 /* Bookmark.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8CA428181B35885F7D9F4D55 /* Bookmark.swift */; };
 		5D86F3F0F603B248776916C7 /* BookmarksViewModel.swift in Sources */ = {isa = PBXBuildFile; fileRef = CBFB5EFC9764B22A2622EA4A /* BookmarksViewModel.swift */; };
 		5ED7F0AB24549BA01757A39C /* PodcastPlayerView.swift in Sources */ = {isa = PBXBuildFile; fileRef = A4EB8C63735A267B81030CB5 /* PodcastPlayerView.swift */; };
+		66D5D90A5FAF842BCA0FE72D /* PodcastRequests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D27A97922BAEBDC9C5A7385C /* PodcastRequests.swift */; };
 		68BDDFF472DDF1854D08A9ED /* AskView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 217E6702DE1210AC38ED16D1 /* AskView.swift */; };
 		6BF0E1F0F4DEAF87B0B8DCF6 /* CollectionsView.swift in Sources */ = {isa = PBXBuildFile; fileRef = FE19F7619214271A8C12EEEB /* CollectionsView.swift */; };
 		706642006800745A0A0188D0 /* RandomBookmarkWidget.swift in Sources */ = {isa = PBXBuildFile; fileRef = 96F73C2A0B8AB36C6F80D5FE /* RandomBookmarkWidget.swift */; };
 		706CCE40744D7F382AFFE429 /* BrowserView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 629C41E0BC28EB6359D50CFD /* BrowserView.swift */; };
 		76223AA04DF97B24C1490B20 /* ShareViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = ADEAC824576633CC77370262 /* ShareViewController.swift */; };
+		773C174263D08416248D0675 /* PodcastGenerationManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = 171EF75BF9BE4592DFA2C716 /* PodcastGenerationManager.swift */; };
 		778B82E075D4DAF5E8446D6F /* BookmarkOnscreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = D1EEDFAE9FCA24192640CA7A /* BookmarkOnscreen.swift */; };
 		8140EEEFBB7A3510A73D1A93 /* SwiftUI.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 093402014727A338745A06DA /* SwiftUI.framework */; };
 		8227B9E3B5EFF6427702F376 /* BookmarkAssistant.swift in Sources */ = {isa = PBXBuildFile; fileRef = E6379451D7FD7090A9F01A01 /* BookmarkAssistant.swift */; };
@@ -33,6 +35,7 @@
 		852A3E18661C190622FF5A85 /* AppIntents.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = F9803BA80BEAE9A3AE4AF5E7 /* AppIntents.framework */; };
 		8BD3FA025C082654D55374A2 /* MarksAuth.swift in Sources */ = {isa = PBXBuildFile; fileRef = F78AA3450BDFAC24591EE407 /* MarksAuth.swift */; };
 		8BDB7DAA6A2711B9499F5582 /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 57D20912C19182A45914069B /* Assets.xcassets */; };
+		8F4BFD6C1322B508E8F52297 /* PodcastRequests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D27A97922BAEBDC9C5A7385C /* PodcastRequests.swift */; };
 		905FBD9468F488ACE4B81726 /* RecentPodcastsWidget.swift in Sources */ = {isa = PBXBuildFile; fileRef = 47CB3AAED5B64809B06A9650 /* RecentPodcastsWidget.swift */; };
 		927BAD5AD47217E3F396CDA7 /* TagsView.swift in Sources */ = {isa = PBXBuildFile; fileRef = B13B9F2D890C7953531AC0D2 /* TagsView.swift */; };
 		94CEF815D51433054412CB20 /* RecentBookmarksWidget.swift in Sources */ = {isa = PBXBuildFile; fileRef = 49C6260D1530C5C4F1AD063E /* RecentBookmarksWidget.swift */; };
@@ -110,6 +113,7 @@
 		093402014727A338745A06DA /* SwiftUI.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = SwiftUI.framework; path = System/Library/Frameworks/SwiftUI.framework; sourceTree = SDKROOT; };
 		0D2CC53B01DF0FE51ADE5FCB /* Marks.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = Marks.entitlements; sourceTree = "<group>"; };
 		0EDC639E0783581A733F4C99 /* WidgetDataStore.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WidgetDataStore.swift; sourceTree = "<group>"; };
+		171EF75BF9BE4592DFA2C716 /* PodcastGenerationManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PodcastGenerationManager.swift; sourceTree = "<group>"; };
 		1A5FEE76168FA5AB1E047FEC /* SpotlightIndexer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SpotlightIndexer.swift; sourceTree = "<group>"; };
 		217E6702DE1210AC38ED16D1 /* AskView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AskView.swift; sourceTree = "<group>"; };
 		22E006A11D594BFC00A9C4B4 /* OnboardingView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OnboardingView.swift; sourceTree = "<group>"; };
@@ -149,6 +153,7 @@
 		CBFB5EFC9764B22A2622EA4A /* BookmarksViewModel.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BookmarksViewModel.swift; sourceTree = "<group>"; };
 		CC6B10FBB227F426A2B597C8 /* BookmarkListRow.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BookmarkListRow.swift; sourceTree = "<group>"; };
 		D1EEDFAE9FCA24192640CA7A /* BookmarkOnscreen.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BookmarkOnscreen.swift; sourceTree = "<group>"; };
+		D27A97922BAEBDC9C5A7385C /* PodcastRequests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PodcastRequests.swift; sourceTree = "<group>"; };
 		D3A4B1E764CC88A774AF8EA5 /* EditBookmarkView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EditBookmarkView.swift; sourceTree = "<group>"; };
 		D6ACABF0CA940312B4195456 /* IntentSupport.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IntentSupport.swift; sourceTree = "<group>"; };
 		D92575C7C710347F226EC74A /* MarksApp.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MarksApp.swift; sourceTree = "<group>"; };
@@ -251,7 +256,9 @@
 				5CCBB391B1E0E1E4EBE0EFC7 /* LinkdingAPI.swift */,
 				FB7728D15C17219ABFF3EFFE /* Log.swift */,
 				F78AA3450BDFAC24591EE407 /* MarksAuth.swift */,
+				171EF75BF9BE4592DFA2C716 /* PodcastGenerationManager.swift */,
 				F75DE8BE4B3A3E0E60B8BB03 /* PodcastIndex.swift */,
+				D27A97922BAEBDC9C5A7385C /* PodcastRequests.swift */,
 				41DDBB04346F3BF06DE233D2 /* SpotlightBookmarkSearch.swift */,
 				1A5FEE76168FA5AB1E047FEC /* SpotlightIndexer.swift */,
 			);
@@ -481,6 +488,7 @@
 				1095DC18A31055ED40CD9323 /* LinkdingAPI.swift in Sources */,
 				B085CDBFC47F0357D1A28911 /* Log.swift in Sources */,
 				B7AF3F940FEE7B8AC32628B6 /* MarksAuth.swift in Sources */,
+				8F4BFD6C1322B508E8F52297 /* PodcastRequests.swift in Sources */,
 				F04066805A33E1A305C11F4F /* ServerConfig.swift in Sources */,
 				8456E89CFE607C2EC57BF466 /* ShareView.swift in Sources */,
 				76223AA04DF97B24C1490B20 /* ShareViewController.swift in Sources */,
@@ -528,8 +536,10 @@
 				E10B0B4EC9580342830EC0D2 /* MarksAppIntents.swift in Sources */,
 				8BD3FA025C082654D55374A2 /* MarksAuth.swift in Sources */,
 				14E1B3CE58D36BFF1A2199C1 /* OnboardingView.swift in Sources */,
+				773C174263D08416248D0675 /* PodcastGenerationManager.swift in Sources */,
 				0479C0AA16E3AFDBD4414AD0 /* PodcastIndex.swift in Sources */,
 				5ED7F0AB24549BA01757A39C /* PodcastPlayerView.swift in Sources */,
+				66D5D90A5FAF842BCA0FE72D /* PodcastRequests.swift in Sources */,
 				EE540B8367519EDE679C1B70 /* SearchView.swift in Sources */,
 				969568D9996EB65550DAA24A /* ServerConfig.swift in Sources */,
 				849C9CB4E1E8A6ABA1BC7251 /* SettingsView.swift in Sources */,