Initial implementation of latent: film-effects editor + develop-later server

Canvas-based client-side editor (grain, vignette, halation, procedural
light leaks, color-cast presets) plus a small Express/SQLite server for
the two paths that need persistence: instant share links and delayed
"send to develop" links with a randomized reveal time.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

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+# latent
+
+A phone-photo editor with a "develop it later" option. Upload a photo,
+apply film-style effects (grain, light leaks, vignette, halation, color
+cast) entirely in the browser, then either download it right away or send
+it off to "develop" — the server holds it behind a randomized delay
+(hours to days) before the link actually resolves to the image. Getting
+your photos back later, on purpose, for no practical reason except that
+it's a fun mechanic.
+
+Named after the *latent image*, the photographic term for the picture
+that already exists on exposed film but is invisible until developed.
+
+See [PROPOSAL.md](PROPOSAL.md) for the original design writeup.
+
+## Two finishing paths off one editor
+
+1. **Instant** — edit, then download directly, entirely client-side.
+   Optionally generate a share link (explicit action, not automatic).
+2. **Delayed** — edit, then "send to develop": uploads to server storage,
+   assigns a random `develop_at` within a configured range, and gives back
+   a link immediately — it just won't resolve to the actual image until
+   that time passes.
+
+## Running locally
+
+```
+npm install --prefix server
+npm start --prefix server
+```
+
+Then open http://localhost:3000. `DATA_DIR` defaults to `./data`
+(gitignored) for the SQLite db and image blobs.
+
+## Deploying
+
+`docker compose up` using the provided `docker-compose.yml` /
+`.env.example` (copy `.env.example` to `.env` and adjust). CI builds and
+pushes the image on push to `main` via `.gitea/workflows/docker.yml`.
+
+## Config
+
+All via env vars, see `.env.example`:
+
+- `DEVELOP_MIN_HOURS` / `DEVELOP_MAX_HOURS` — randomized delay range for
+  the "send to develop" path (default 2–48h).
+- `INSTANT_TTL_HOURS` — retention for share links off the instant path
+  (default 24h; deliberately shorter than the delayed path since it's a
+  more casual "just give me a link" flow).
+- `DELAYED_VIEW_WINDOW_HOURS` — how long a delayed image stays available
+  *after* `develop_at` passes, before the TTL sweep deletes it (default
+  168h / 7 days).
+- `MAX_UPLOAD_BYTES`, `RATE_LIMIT_PER_HOUR` — basic abuse limits; no
+  accounts or auth on any endpoint, the link itself is the credential.
+
+## Non-goals
+
+No accounts, no galleries, no e2e encryption (nothing here is sensitive —
+the whole point is a link other people can open), no collaborative
+editing.