Build your own ephemeral snap relay (a personal Snapchat)

Build the project scaffold for a private snap relay. Requirements:
- Node 22 + Fastify + better-sqlite3 with WAL mode, no build step, static files served from /public.
- Vanilla-JS installable PWA: manifest.json plus a service worker that caches the UI shell for offline but never caches snap images.
- Invite-code accounts: scripts/seed-invites.js writes codes into SQLite, signup is username plus passcode, sessions are httpOnly cookies.
- Media lives as files in ./data/media outside the web root; metadata in ./data/app.db.
- SESSION_SECRET in .env, with .env.example and a scripts/gen-secrets.js that generates values.
- Local dev over HTTPS with a self-signed cert; document the browser warning and the trust step in README.
- Out of scope: styling polish, third-party auth, any test runner beyond node:test.
- Verify: npm start serves https://localhost:8443 and signup with a seeded code creates a row in the users table.

Add the snap capture and send flow. Requirements:
- Open the camera with getUserMedia, front or rear, and capture a still to a canvas.
- Caption layer: type text or draw with a finger on the same canvas, flattened to one JPEG on send.
- POST the JPEG to /api/snaps with a recipient list; the server writes the file to ./data/media and one row per recipient in a snaps table.
- Recipient picker lists users created via the step 1 invite flow.
- Export JPEG at quality 0.8 to keep uploads near 2 MB, phones on weak connections stall on full-resolution images.
- Out of scope: video capture, filters of any kind.
- Verify: send a snap to yourself from a phone on your network and watch the file appear in ./data/media.

Add view-once delivery and per-pair streaks. Requirements:
- GET /api/snaps/:id streams the image once, marks the row opened, then deletes the file immediately; only sent and opened timestamps remain.
- Client shows the snap full-screen for up to 10 seconds then returns to the inbox; reopening shows 'deleted from our server'.
- Streaks table keyed on the sorted user pair, incremented once per calendar day when both directions have sent.
- Day-boundary math uses the server clock in one documented timezone, mixing client and server clocks here causes phantom streak breaks.
- Tests with node:test and a fake clock: delete-after-view removes the file, and a streak survives a send at 23:59 answered at 00:01.
- Honest UI copy: state plainly that screenshots cannot be detected on the web.
- Out of scope: read receipts beyond the opened flag, resend or retry queues.

Add 24-hour group stories. Requirements:
- POST /api/story adds a snap visible to all members; story rows live in a stories table pointing at files in ./data/media.
- A sweep job runs every 10 minutes and hard-deletes story files and rows older than 24 hours.
- Story viewer shows items oldest first with tap-to-advance.
- Sweep test using the step 3 fake clock: an item aged 23h50m survives, one aged 24h10m is gone, both file and row.
- Log each sweep run with a deleted-item count so you can verify it on the server later.
- Out of scope: per-viewer watch receipts, story replies.

Add web push notifications for new snaps and stories. Requirements:
- Use the web-push library with VAPID keys generated by scripts/gen-secrets.js from step 1 and stored in .env.
- Request permission only after the user sends their first snap, never on first load; store subscriptions in a push_subs table.
- Notify recipients on new snaps and story posts; a failed push must never block or delay the send itself.
- Full functionality with push denied; README states iOS web push is best-effort.
- Test: a subscription returning HTTP 410 is pruned from push_subs.
- Out of scope: notification preference UI, unread badge counts.