Initial implementation of SwiftDBAI

Chat with any SQLite database using natural language. Built on
AnyLanguageModel (HuggingFace) for LLM-agnostic provider support
and GRDB for SQLite access.

Core features:
- Auto schema introspection from sqlite_master (zero config)
- NL → SQL generation via any AnyLanguageModel provider
- Three rendering modes: text summary, data table, Swift Charts
- Drop-in DataChatView (SwiftUI) and headless ChatEngine
- Operation allowlist with read-only default
- Mutation policy with per-table control
- ToolExecutionDelegate for destructive operation confirmation
- Multi-turn conversation context
- 352 tests across 24 suites, all passing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,7 @@
+.build/
+.swiftpm/
+Package.resolved
+*.xcodeproj/
+xcuserdata/
+DerivedData/
+.DS_Store