fix: resolve Greptile P1 close() timer leak, engine git init, dashboard test

- store.ts close(): clear retry timer and buffer before nulling _db to
  prevent re-opening a new connection after close (Greptile P1)
- merger-staging-allowlist.test.ts: use `git init -b main` so the
  default branch is always named 'main' regardless of git config
- SettingsModal.test.tsx: fix expected text for compact DroidCli card
  — shows "✓ Active" badge, not "✓ Connected — 1.2.3"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/dashboard/app/components/__tests__/SettingsModal.test.tsx

@@ -1097,7 +1097,7 @@ describe("SettingsModal", () => {
           extension: { status: "ok" },
           ready: true,
         },
-        expectedText: "✓ Connected — 1.2.3",
+        expectedText: "✓ Active",
       },
     ])("renders plugin-driven droid card state: $name", async ({ status, expectedText }) => {
       mockFetchAuthStatus.mockResolvedValueOnce({