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

hermes_cli/config.py

@@ -64,6 +64,7 @@ def ensure_hermes_home():
     (home / "cron").mkdir(parents=True, exist_ok=True)
     (home / "sessions").mkdir(parents=True, exist_ok=True)
     (home / "logs").mkdir(parents=True, exist_ok=True)
+    (home / "memories").mkdir(parents=True, exist_ok=True)
 
 
 # =============================================================================
@@ -128,11 +129,19 @@ DEFAULT_CONFIG = {
         "max_ms": 2500,
     },
     
+    # Persistent memory -- bounded curated memory injected into system prompt
+    "memory": {
+        "memory_enabled": True,
+        "user_profile_enabled": True,
+        "memory_char_limit": 2200,   # ~800 tokens at 2.75 chars/token
+        "user_char_limit": 1375,     # ~500 tokens at 2.75 chars/token
+    },
+    
     # Permanently allowed dangerous command patterns (added via "always" approval)
     "command_allowlist": [],
     
     # Config schema version - bump this when adding new required fields
-    "_config_version": 2,
+    "_config_version": 3,
 }
 
 # =============================================================================