Make the frontend an installable PWA

Add a web app manifest and an install-only service worker (no offline
caching: live state always comes from the server and hashed asset names
change every build), registered from the WASM bundle. The worker must
live at the site root for its scope to cover the app, and Granian only
serves /static and /assets, so tavolo/static.py answers
/manifest.webmanifest and /sw.js from STATIC_DIR with the content types
browsers require; index.html gains the manifest link, icons, theme-color
and Apple standalone meta tags.

Icons are committed under web/assets/icons/ with vector sources and a
make-icons.sh regeneration script, mirroring the card art workflow.

server/Dockerfile

@@ -30,6 +30,9 @@ WORKDIR /web
 # Card images are committed in the repository (CC0 woodcut napoletane deck);
 # web/fetch-cards.sh can regenerate them.
 COPY web/Cargo.toml web/Cargo.lock web/index.html web/style.css web/theme.css web/Trunk.toml ./
+# PWA manifest and service worker: trunk's copy-file entries need them at
+# the build root, and the runtime serves both from the site root (static.py).
+COPY web/manifest.webmanifest web/sw.js ./
 COPY web/assets ./assets
 # Vendored Bootstrap (MIT) loaded by index.html; kept out of the CDN so the
 # image builds and runs without network access.