feat: opt-in state.db sync for /insights visibility (#92)

WebUI sessions were invisible to 'hermes /insights' because the WebUI
bypasses the gateway and calls AIAgent.run_conversation() directly,
never writing to state.db.

New 'Sync usage to /insights' setting (default: off) that mirrors
WebUI session metadata (tokens, cost, model, title) into state.db
after each turn. Uses absolute token counts to avoid double-counting.

Components:
- api/state_sync.py: bridge module with sync_session_start() and
  sync_session_usage(). Uses ensure_session() (idempotent) and
  update_token_counts(absolute=True). All wrapped in try/except.
- api/config.py: new 'sync_to_insights' boolean setting
- api/streaming.py: calls sync_session_usage() after s.save()
- api/routes.py: same for the non-streaming chat path
- Settings UI: checkbox toggle with description

Default off because:
- Writing to state.db while CLI/gateway also writes could cause
  WAL lock contention on busy systems
- Some users may not want WebUI sessions in /insights stats

Closes #92

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/state_sync.py

@@ -0,0 +1,93 @@
+"""
+Hermes Web UI -- Optional state.db sync bridge.
+
+Mirrors WebUI session metadata (token usage, title, model) into the
+hermes-agent state.db so that /insights, session lists, and cost
+tracking include WebUI activity.
+
+This is opt-in via the 'sync_to_insights' setting (default: off).
+All operations are wrapped in try/except -- if state.db is unavailable,
+locked, or the schema doesn't match, the WebUI continues normally.
+
+The bridge uses absolute token counts (not deltas) because the WebUI
+Session object already accumulates totals across turns. This avoids
+any double-counting risk.
+"""
+import os
+from pathlib import Path
+
+
+def _get_state_db():
+    """Get a HermesState instance for the active profile's state.db.
+    Returns None if hermes_state is not importable or DB is unavailable.
+    """
+    try:
+        from hermes_state import HermesState
+    except ImportError:
+        return None
+
+    try:
+        from api.profiles import get_active_hermes_home
+        hermes_home = Path(get_active_hermes_home()).expanduser().resolve()
+    except Exception:
+        hermes_home = Path(os.getenv('HERMES_HOME', str(Path.home() / '.hermes')))
+
+    db_path = hermes_home / 'state.db'
+    if not db_path.exists():
+        return None
+
+    try:
+        return HermesState(str(db_path))
+    except Exception:
+        return None
+
+
+def sync_session_start(session_id, model=None):
+    """Register a WebUI session in state.db (idempotent).
+    Called when a session's first message is sent.
+    """
+    try:
+        db = _get_state_db()
+        if not db:
+            return
+        db.ensure_session(
+            session_id=session_id,
+            source='webui',
+            model=model,
+        )
+    except Exception:
+        pass  # never crash the WebUI for sync failures
+
+
+def sync_session_usage(session_id, input_tokens=0, output_tokens=0,
+                       estimated_cost=None, model=None, title=None):
+    """Update token usage and title for a WebUI session in state.db.
+    Called after each turn completes. Uses absolute=True to set totals
+    (the WebUI Session already accumulates across turns).
+    """
+    try:
+        db = _get_state_db()
+        if not db:
+            return
+        # Ensure session exists first (idempotent)
+        db.ensure_session(session_id=session_id, source='webui', model=model)
+        # Set absolute token counts
+        db.update_token_counts(
+            session_id=session_id,
+            input_tokens=input_tokens,
+            output_tokens=output_tokens,
+            estimated_cost_usd=estimated_cost,
+            model=model,
+            absolute=True,
+        )
+        # Update title if we have one
+        if title:
+            try:
+                db._execute_write(
+                    "UPDATE sessions SET title = ? WHERE id = ?",
+                    (title, session_id),
+                )
+            except Exception:
+                pass
+    except Exception:
+        pass  # never crash the WebUI for sync failures