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>

.env.example

@@ -0,0 +1,22 @@
+# Copy to .env to override docker-compose.yml defaults.
+
+# Image to deploy — set by CI/CD normally; only needed for a manual
+# docker compose up.
+IMAGE=repo.explewd.com/explewd/latent:latest
+
+# Host port to expose (container always listens on 3000).
+HOST_PORT=3050
+
+# Randomized "send to develop" delay range, in hours.
+DEVELOP_MIN_HOURS=2
+DEVELOP_MAX_HOURS=48
+
+# Retention. Instant/share-link images are a casual "just give me a link"
+# flow and get a shorter TTL; delayed images must stay alive past
+# develop_at with room to actually go view them, so their window is
+# measured from develop_at, not upload time.
+INSTANT_TTL_HOURS=24
+DELAYED_VIEW_WINDOW_HOURS=168
+
+MAX_UPLOAD_BYTES=20971520
+RATE_LIMIT_PER_HOUR=30