Add Sycamore/WASM frontend and restructure into server/ + web/

Repo is now a monorepo:

- server/: the kaya backend, unchanged in behaviour, plus:
  - GET /api/me for SPA session detection
  - last_move recorded on every play and broadcast in the game state, so
    clients can show who played which card the moment they play it
  - legal_moves per hand card for the player on turn (rules stay
    server-side)
  - static catch-all route serving the compiled SPA with index.html
    fallback; Tortoise context now bound only for /api/* requests
  - configurable OIDC post-login/logout redirects for dev against trunk
- web/: Sycamore 0.9 + WASM frontend (trunk): login via the OIDC flow,
  lobby (create match / join by code), live game page over websocket with
  card images (CC0 woodcut napoletane deck), capture picker, move banner,
  game-over overlay, match history and leaderboard pages
- server/Dockerfile gains a rust+trunk stage building web/dist; the single
  app image serves the SPA; compose builds from the repo root with
  overridable ports/OIDC env

Verified end-to-end against the compose stack: four OIDC logins, game
creation, three joins by code, websocket play with broadcasts to all
players and out-of-turn rejection. 51 backend tests, mypy and cargo tests
all green.

web/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "scopa-web"
+version = "0.1.0"
+edition = "2021"
+description = "Sycamore/WASM frontend for the scopone scientifico backend"
+
+[dependencies]
+sycamore = "0.9"
+sycamore-router = "0.9"
+gloo-net = { version = "0.6", features = ["websocket"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+wasm-bindgen = "0.2"
+wasm-bindgen-futures = "0.4"
+futures = "0.3"
+web-sys = { version = "0.3", features = ["Window", "Location", "console"] }
+console_error_panic_hook = "0.1"
+
+[profile.release]
+opt-level = "z"
+lto = true