fix(plugins): register all SQLite file extensions end-to-end (#1327)

[datlechin]

Summary

Closes #1327 (.db not registered as SQLite document type — Finder "Open With" grays out TablePro).

The reported gap was .db, but auditing the codebase surfaced the opposite-direction gap as well: TablePro's Info.plist and the SQLite plugin had different SQLite extension lists, and neither was a superset of the other.

Source	Before
Info.plist (CFBundleDocumentTypes + UTExportedTypeDeclarations)	sqlite, sqlite3, db3, s3db, sl3, sqlitedb
SQLitePlugin.swift + PluginMetadataRegistry	db, sqlite, sqlite3

Two real bugs from this mismatch:

1. .db files missing from Info.plist → Finder "Open With" grays out TablePro (the reported issue).
2. .db3 / .s3db / .sl3 / .sqlitedb files claimed by Info.plist but not registered in the plugin's extension map → URLClassifier.swift:37 returns nil from classifyFile(...), so double-clicking these files in Finder launches TablePro but silently fails to open them. This was a latent bug nobody had reported yet.

Fix: pick the union in all four locations: db, db3, s3db, sl3, sqlite, sqlite3, sqlitedb. Plus mobile parity.

Files changed

• TablePro/Info.plist — added db to CFBundleDocumentTypes and UTExportedTypeDeclarations (the second one is what tells Launch Services TablePro can handle the type)
• Plugins/SQLiteDriverPlugin/SQLitePlugin.swift — extension list now ["db", "db3", "s3db", "sl3", "sqlite", "sqlite3", "sqlitedb"]
• TablePro/Core/Plugins/PluginMetadataRegistry.swift — same list, the registry's runtime map for URLClassifier
• TableProMobile/.../ConnectionFormView.swift — file picker now allows all 7 extensions instead of hardcoding sqlite3 only
• CHANGELOG.md — one Fixed entry under Unreleased

Verification

• Build clean (only pre-existing third-party SwiftLint failures, unrelated)
• No banned filler in diff
• No new dependencies, no new pasteboard or UTI declarations beyond extending an existing one

Test plan

• Save a SQLite database with a .db extension (e.g., the Chinook sample). Right-click in Finder → Open With → TablePro is offered, not grayed out.
• Same for .db3, .s3db, .sl3, .sqlitedb files.
• Double-click any of the 7 extensions on a real SQLite file — TablePro opens it as a database connection (previously only .sqlite/.sqlite3 worked reliably).
• On iOS, open the connection form and tap the SQLite file picker — .db files are now selectable.