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-timeline-query.ts

@@ -0,0 +1,67 @@
+import { SessionStore } from '../src/services/sqlite/SessionStore.js';
+
+const store = new SessionStore();
+
+console.log('=== Test 1: Without project filter ===');
+try {
+  const result = store.getTimelineAroundTimestamp(
+    1730667961000, // timestamp for observation 3300
+    5,
+    5
+  );
+
+  console.log('Result:', {
+    observations: result?.observations?.length,
+    sessions: result?.sessions?.length,
+    prompts: result?.prompts?.length
+  });
+} catch (err) {
+  console.error('ERROR:', err);
+}
+
+console.log('\n=== Test 2: With project filter ===');
+try {
+  const result = store.getTimelineAroundTimestamp(
+    1730667961000,
+    5,
+    5,
+    'claude-mem'
+  );
+
+  console.log('Result:', {
+    observations: result?.observations?.length,
+    sessions: result?.sessions?.length,
+    prompts: result?.prompts?.length
+  });
+} catch (err) {
+  console.error('ERROR:', err);
+}
+
+console.log('\n=== Test 3: With actual observation ID ===');
+// First get the actual timestamp for observation 3300
+const obs = store.getObservationById(3300);
+console.log('Observation 3300:', obs ? `Found at epoch ${obs.created_at_epoch}` : 'Not found');
+
+if (obs) {
+  try {
+    const result = store.getTimelineAroundTimestamp(
+      obs.created_at_epoch,
+      5,
+      5
+    );
+
+    console.log('Result:', {
+      observations: result?.observations?.length,
+      sessions: result?.sessions?.length,
+      prompts: result?.prompts?.length
+    });
+
+    console.log('Observations:', result.observations?.map(o => `#${o.id}`));
+    console.log('Sessions:', result.sessions?.map(s => `#S${s.id}`));
+    console.log('Prompts:', result.prompts?.map(p => `#P${p.id}`));
+  } catch (err) {
+    console.error('ERROR:', err);
+  }
+}
+
+store.close();