Add iOS Ask AI experience and supporting integration updates

[humandebri]

Summary

• Add the iOS Ask AI conversation, retrieval, evidence, tracing, and history experience
• Integrate knowledge retrieval with VFS and Internet Identity-backed database access
• Add share-extension source capture and shared inbox/history handling
• Add comprehensive Ask AI, retrieval, sharing, and model tests
• Update CI, smoke-test documentation, app configuration, and App Store assets

Testing

• Added and updated Swift unit tests covering Ask AI flows, response decoding, retrieval planning, sharing, persistence, and VFS codecs
• Updated Rust integration and contract tests for the related storage behavior
• CI and public smoke-test documentation updated