Forum content search fts5

[jolavillette]

Code and comment by AI

Forum Deep Search (FTS5 Integration) - Core Logic

This PR implements the core backend for the Forum Content Search feature using the SQLite FTS5 extension.

Key Changes

• FTS5 Engine: Implementation of DeepForumsIndexFTS5 in src/deep_search/. This engine handles full-text indexing and searching for forum groups and messages.
• Secure Storage: The search index is stored in a dedicated SQLite database, encrypted using SQLCipher with the standard GXS keys.
• Service Integration:
  • Updated p3gxsforums to orchestrate indexing and search queries.
  • Enhanced p3wire for internal signaling and potential future sync metadata.
• Database Utilities: Extended RetroDb and rsdataservice to support the specific requirements of the FTS5 encrypted index.
• Serialization: Updated TLV serializers in src/serialiser/ to ensure forward compatibility with search-related metadata.

Verification

• Unit tests for FTS5 table creation, indexing, and weighted search results.
• Verification of database encryption at rest.