fix(docker): give web/ a tracked file so the build stage can copy it

git does not track empty directories, so COPY web/ ./ failed on a clean
checkout with "/web: not found" — the Dockerfile built locally, where
the directory exists, and only in CI.

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

web/README.md

@@ -0,0 +1,34 @@
+# web
+
+The SvelteKit PWA. Not written yet — this directory holds its place so the Docker
+build has something to copy, and so the frontend stage can tell "not built yet"
+apart from "the build failed".
+
+The Dockerfile builds this directory when it finds a `package.json` here, and
+otherwise emits a placeholder page. So adding the real app is exactly: put a
+SvelteKit project in this directory whose `npm run build` produces `build/`.
+
+## What it needs to be
+
+- **SvelteKit**, `adapter-static`, output in `build/`. The Go binary embeds that
+  directory at compile time and serves it, falling back to `index.html` so
+  client-side routes survive a reload.
+- **A PWA**: installable, offline reading of already-cached lists, swipe gestures
+  for complete and schedule.
+- **Nordic minimalism.** Dark by default, light available. One accent colour,
+  everything else neutral. Runic mark for Verdande.
+- **Optimistic on every local action.** No spinner ever appears for something the
+  browser could already know the answer to.
+
+## Talking to the backend
+
+Same origin — the Go binary serves both. `/api/v1` for REST, `/api/v1/ws` for the
+live sync. Session cookie is `httpOnly`, so the frontend never handles the token
+itself.
+
+During development, run the backend on 8080 and point the Vite dev server's proxy
+at it:
+
+```bash
+VERDANDE_DATA_DIR=./data VERDANDE_DEV=true go run ./cmd/verdande
+```