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

README.md

@@ -154,7 +154,35 @@ hermes --toolsets "web,terminal"
 hermes --list-tools
 ```
 
-**Available toolsets:** `web`, `terminal`, `file`, `browser`, `vision`, `image_gen`, `moa`, `skills`, `tts`, `todo`, `cronjob`, and more.
+**Available toolsets:** `web`, `terminal`, `file`, `browser`, `vision`, `image_gen`, `moa`, `skills`, `tts`, `todo`, `memory`, `session_search`, `cronjob`, and more.
+
+### 🧠 Persistent Memory
+
+Bounded curated memory that persists across sessions:
+
+- **MEMORY.md** — agent's personal notes (environment facts, conventions, things learned). ~800 token budget.
+- **USER.md** — user profile (preferences, communication style, expectations). ~500 token budget.
+
+Both are injected into the system prompt as a frozen snapshot at session start. The agent manages its own memory via the `memory` tool (add/replace/remove/read). Character limits keep memory focused — when full, the agent consolidates or replaces entries.
+
+Configure in `~/.hermes/config.yaml`:
+```yaml
+memory:
+  memory_enabled: true
+  user_profile_enabled: true
+  memory_char_limit: 2200   # ~800 tokens
+  user_char_limit: 1375     # ~500 tokens
+```
+
+### 🗄️ Session Store
+
+All CLI and messaging sessions are stored in a SQLite database (`~/.hermes/state.db`) with full-text search:
+
+- **Full message history** stored per-session with model config and system prompt snapshots
+- **FTS5 search** via the `session_search` tool -- search past conversations with Gemini Flash summarization
+- **Compression-triggered session splitting** -- when context is compressed, a new session is created linked to the parent, giving clean trajectories
+- **Source tagging** -- each session is tagged with its origin (cli, telegram, discord, etc.)
+- Batch runner and RL trajectories are NOT stored here (separate systems)
 
 ### 🔊 Text-to-Speech