Apply WWDC26 design-brief fixes to the bookmark list reading surface:
- Dynamic Type: replace fixed .system(size:) points with text styles
(title .headline, domain/date .footnote, summary .subheadline, tags
.caption, podcast glyph .title3). Rows now scale and wrap with the
user's text-size setting instead of staying fixed.
- Perf: podcastCached was a FileManager.fileExists stat evaluated inside
body — i.e. per row, per scroll frame. Move it to @State populated by a
.task(id:) that stats off the main actor, once per appearance.
- Forgiveness: destructive trailing swipe is now allowsFullSwipe: false so
a single fling can't permanently delete; requires tapping the button.
Adds docs/design-wwdc26.md (consolidated brief + codebase audit).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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