feat(app): embed indexer in Electron with file-watching service and UI refinements

Extract schema DDL into scripts/schema.sql shared between CLI and app.
  Add an in-process chokidar-based indexer-service that watches ~/.claude/projects
  for JSONL changes, debounces, and triggers background rebuilds via a worker
  thread. Rename Usage view to Activity, flesh out MemoryDetail and SubagentDetail
  views, and refine App.vue layout/routing. The main process now starts/stops the
  indexer lifecycle and notifies renderer windows on index updates.

app/indexer-worker.js

@@ -0,0 +1,17 @@
+const { parentPort } = require('worker_threads');
+const { buildIndex } = require('./indexer');
+
+parentPort.on('message', ({ id, args }) => {
+  try {
+    const result = buildIndex(args || {});
+    parentPort.postMessage({ id, result });
+  } catch (error) {
+    parentPort.postMessage({
+      id,
+      error: {
+        message: error.message,
+        stack: error.stack,
+      },
+    });
+  }
+});