feat: Implement user prompt syncing to Chroma and enhance timeline querying

- Added `getObservationById` method to retrieve observations by ID in SessionStore.
- Introduced `getSessionSummariesByIds` and `getUserPromptsByIds` methods for fetching session summaries and user prompts by IDs.
- Developed `getTimelineAroundTimestamp` and `getTimelineAroundObservation` methods to provide a unified timeline of observations, sessions, and prompts around a specified anchor point.
- Enhanced ChromaSync to format and sync user prompts, including a new `syncUserPrompt` method.
- Updated WorkerService to sync the latest user prompt to Chroma after updating the worker port.
- Created tests for timeline querying and MCP handler logic to ensure functionality.
- Documented the implementation plan for user prompts and timeline context tool in the Chroma search completion plan.

experiment/test-mcp-direct.js

@@ -0,0 +1,54 @@
+import { SessionStore } from '../src/services/sqlite/SessionStore.js';
+
+const store = new SessionStore();
+
+// Simulate what the MCP handler does
+const args = {
+  anchor: 3300,
+  depth_before: 10,
+  depth_after: 10
+};
+
+console.log('Testing MCP handler logic with anchor:', args.anchor);
+
+try {
+  let timeline;
+  const anchor = args.anchor;
+  const depth_before = args.depth_before;
+  const depth_after = args.depth_after;
+
+  if (typeof anchor === 'number') {
+    console.log('Anchor is number, getting observation...');
+    const obs = store.getObservationById(anchor);
+    if (!obs) {
+      console.error('Observation not found!');
+      process.exit(1);
+    }
+    console.log('Found observation:', obs.id, 'at epoch:', obs.created_at_epoch);
+
+    console.log('Calling getTimelineAroundObservation...');
+    timeline = store.getTimelineAroundObservation(anchor, obs.created_at_epoch, depth_before, depth_after);
+
+    console.log('Timeline result:', {
+      observations: timeline.observations?.length,
+      sessions: timeline.sessions?.length,
+      prompts: timeline.prompts?.length
+    });
+
+    console.log('Timeline observations type:', typeof timeline.observations);
+    console.log('Timeline sessions type:', typeof timeline.sessions);
+    console.log('Timeline prompts type:', typeof timeline.prompts);
+
+    if (timeline.observations) {
+      console.log('First observation:', timeline.observations[0]);
+    }
+  }
+
+  console.log('\n✓ No errors!');
+} catch (err) {
+  console.error('ERROR:', err.message);
+  console.error(err.stack);
+  process.exit(1);
+}
+
+store.close();