Adapts three more memory backend PRs to the MemoryProvider interface:
OpenViking (PR #3369 by Mibayy):
- 3 tools: viking_search, viking_read, viking_browse
- Read-only, self-hosted server, no sync/prefetch
- URI-based content with progressive disclosure levels
RetainDB (PR #2732 by Alinxus):
- 5 tools: retaindb_profile, retaindb_search, retaindb_context,
retaindb_remember, retaindb_forget
- Cloud API with prefetch, sync, and memory bridging
- Durable write-behind queue pattern
Cognitive Memory (PR #727 by 0xbyt4):
- 1 tool with 4 actions: recall, store, forget, status
- Local SQLite with vector embeddings (litellm)
- Auto-classification, importance decay, dedup, forgetting
All gated on credentials/deps via is_available():
- OpenViking: OPENVIKING_ENDPOINT + server health check
- RetainDB: RETAINDB_API_KEY
- Cognitive: litellm importable (uses its env vars for embedding API)
