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

scripts/install.sh

@@ -614,7 +614,7 @@ copy_config_templates() {
     log_info "Setting up configuration files..."
     
     # Create ~/.hermes directory structure (config at top level, code in subdir)
-    mkdir -p "$HERMES_HOME"/{cron,sessions,logs,pairing,hooks,image_cache,audio_cache}
+    mkdir -p "$HERMES_HOME"/{cron,sessions,logs,pairing,hooks,image_cache,audio_cache,memories}
     
     # Create .env at ~/.hermes/.env (top level, easy to find)
     if [ ! -f "$HERMES_HOME/.env" ]; then