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

docs/tools.md

@@ -48,6 +48,8 @@ async def web_search(query: str) -> dict:
 | **Reasoning** | `mixture_of_agents_tool.py` | `mixture_of_agents` |
 | **Skills** | `skills_tool.py` | `skills_list`, `skill_view` |
 | **Todo** | `todo_tool.py` | `todo` (read/write task list for multi-step planning) |
+| **Memory** | `memory_tool.py` | `memory` (persistent notes + user profile across sessions) |
+| **Session Search** | `session_search_tool.py` | `session_search` (search + summarize past conversations) |
 | **Cronjob** | `cronjob_tools.py` | `schedule_cronjob`, `list_cronjobs`, `remove_cronjob` |
 | **RL Training** | `rl_training_tool.py` | `rl_list_environments`, `rl_start_training`, `rl_check_status`, etc. |
 
@@ -90,6 +92,10 @@ TOOLSETS = {
         "description": "Task planning and tracking for multi-step work",
         "tools": ["todo"]
     },
+    "memory": {
+        "description": "Persistent memory across sessions (personal notes + user profile)",
+        "tools": ["memory"]
+    },
     # ...
 }
 ```