feat: add persistent memory system + SQLite session store

Two-part implementation:

Part A - Curated Bounded Memory:
- New memory tool (tools/memory_tool.py) with MEMORY.md + USER.md stores
- Character-limited (2200/1375 chars), § delimited entries
- Frozen snapshot injected into system prompt at session start
- Model manages pruning via replace/remove with substring matching
- Usage indicator shown in system prompt header

Part B - SQLite Session Store:
- New hermes_state.py with SessionDB class, FTS5 full-text search
- Gateway session.py rewritten to dual-write SQLite + legacy JSONL
- Compression-triggered session splitting with parent_session_id chains
- New session_search tool with Gemini Flash summarization of matched sessions
- CLI session lifecycle (create on launch, close on exit)

Also:
- System prompt now cached per session, only rebuilt on compression
  (fixes prefix cache invalidation from date/time changes every turn)
- Config version bumped to 3, hermes doctor checks for new artifacts
- Disabled in batch_runner and RL environments

environments/agent_loop.py

@@ -328,6 +328,12 @@ class HermesAgentLoop:
                                     store=_todo_store,
                                 )
                                 tool_elapsed = _time.monotonic() - tool_submit_time
+                            elif tool_name == "memory":
+                                tool_result = json.dumps({"error": "Memory is not available in RL environments."})
+                                tool_elapsed = _time.monotonic() - tool_submit_time
+                            elif tool_name == "session_search":
+                                tool_result = json.dumps({"error": "Session search is not available in RL environments."})
+                                tool_elapsed = _time.monotonic() - tool_submit_time
                             else:
                                 # Run tool calls in a thread pool so backends that
                                 # use asyncio.run() internally (modal, docker) get