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.

server/dev/mockoauth/Dockerfile

@@ -0,0 +1,9 @@
+# Dev OIDC provider: navikt/mock-oauth2-server with the scopa test
+# configuration (four ready-made players) baked in. The config is
+# COPYed instead of bind-mounted so this also works against containerized
+# (e.g. rootless/DinD) docker daemons that cannot see the host workspace.
+FROM ghcr.io/navikt/mock-oauth2-server:5.0.2
+
+COPY config.json /config.json
+
+ENV JSON_CONFIG_PATH=/config.json

server/dev/mockoauth/config.json

@@ -0,0 +1,55 @@
+{
+  "interactiveLogin": true,
+  "tokenCallbacks": [
+    {
+      "issuerId": "scopa",
+      "tokenExpiry": 3600,
+      "requestMappings": [
+        {
+          "requestParam": "subject",
+          "match": "alice",
+          "claims": {
+            "sub": "alice",
+            "preferred_username": "alice",
+            "name": "Alice"
+          }
+        },
+        {
+          "requestParam": "subject",
+          "match": "bob",
+          "claims": {
+            "sub": "bob",
+            "preferred_username": "bob",
+            "name": "Bob"
+          }
+        },
+        {
+          "requestParam": "subject",
+          "match": "carol",
+          "claims": {
+            "sub": "carol",
+            "preferred_username": "carol",
+            "name": "Carol"
+          }
+        },
+        {
+          "requestParam": "subject",
+          "match": "dave",
+          "claims": {
+            "sub": "dave",
+            "preferred_username": "dave",
+            "name": "Dave"
+          }
+        },
+        {
+          "requestParam": "subject",
+          "match": ".*",
+          "claims": {
+            "sub": "${subject}",
+            "preferred_username": "${subject}"
+          }
+        }
+      ]
+    }
+  ]
+}