Improve session UI, model favorites, and changes navigation

[eivindjonassen]

Summary

• Render Markdown natively with tables, nested formatting, safe links, and horizontally scrollable code; improve tool cards and model/runtime footers.
• Show session titles and Session/Changes tabs beside the branch, with connection notices only when needed. Keep app updates in Settings.
• Add searchable model/agent pickers, compact variant sheets, accessible selection controls, and connection-scoped model favorites with schema v12 migration.
• Present collapsed changed-file rows with counts and expandable diffs.
• Add a safe-area provider inside native modal sheets to address picker headers overlapping the iOS status bar before search focus.
• Extend confirmed-missing worktree retirement to registered sandboxes while preserving history and attention. Document the recent-session display limit.

Validation

• pnpm check passed: lint, typecheck, 369 mobile tests, adapter/package tests, and both iOS/Android Hermes exports.
• pnpm native:doctor passed all 18 checks.
• Native fingerprints matched installed runtime 0.1.4 before preview OTA publication.
• Published preview update: https://expo.dev/accounts/omnicus/projects/o5s-code/updates/810d32a8-b209-4ba1-a210-a0d537091c31
• On-device confirmation of the latest modal safe-area fix is pending. Automated tests do not verify native visual layout.