Architecture extensibility — event bus, middleware, auto-discovery, Pydantic profiles ...

- EventBus: async pub/sub for AgentEvents, WebSocket subscribes instead of direct yield
- Declarative serialization: AgentEvent.to_wire() on all event types
- Auto-discovery for LLM backends (_discover_backends) and workers (scan navi/workers/*.py)
- AgentProfile: Pydantic BaseModel with extra='allow', @field_validator for model coercion
- Tool middleware chain: pre/post execute hooks via ToolRegistry.add_middleware()
- LoggingMiddleware: built-in, logs every tool call
- Fix pg_trgm DDL: conditional GIN indexes via DO $$ block, no CREATE EXTENSION
- New files: event_bus.py, middleware.py, logging_middleware.py

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Architecture fixes batch — NaN validation, ILIKE indexes, prompt cache, N+1 batching ...

- _vector_to_str: reject NaN/Inf via math.isfinite() to avoid invalid pgvector syntax
- memory DDL: add pg_trgm + GIN trigram indexes on category/key/value for fast ILIKE fallback
- _build_system_prompt: cache per-profile to avoid rebuilding every iteration
- backfill_embeddings: batch UPDATEs via executemany instead of N+1 loop

No new Python deps; pg_trgm is a PostgreSQL extension auto-created on startup.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Clean up SQLite references in docs and prompts after removal ...

- docs/index.md: PostgreSQL via asyncpg
- docs/memory.md: drop aiosqlite fallback mention
- docs/sessions.md: replace SqliteSessionStore with PgSessionStore docs
- webclient/docs/architecture.md: PostgreSQL only
- navi/profiles/tool_developer/system_prompt.txt: remove aiosqlite from available imports
- .gitignore: add .codex and *.db
- No remaining sqlite/aiosqlite/db_path references in codebase

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Update memory docs to reflect pgvector + dedicated embedding backend ...

- Add dedicated embedding backend section (.env variables)
- Add backfill_embeddings script documentation
- Update storage methods: upsert_fact generates embeddings, search_facts
  uses vector search with cosine distance fallback to ILIKE
- Update extractor process: tool calls/results in transcript, source/confidence
- Replace memory_search/memory_forget references with unified memory tool

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Document pgvector migration in memory system ...

- Add PostgreSQL vs SQLite comparison table

- Document migrate_pgvector.py usage

- Update storage section to mention asyncpg + aiosqlite

Add backend documentation ...

10 markdown files covering all backend subsystems: architecture,
agent loop, tool system, sessions, WebSocket protocol, profiles,
memory, config, and API reference. Structured for AI readability
with a single entry point (docs/index.md) and cross-references.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>