Add GetPlayerID, GetUserID, GetNickname to the sessions package.
Remove the inline player-ID-from-session pattern duplicated across
every handler in c4game and snakegame, and the local getPlayerID
helper in snakegame.
Replace CDN-hosted datastar beta.11 with local v1.0.0-RC.7 to fix
client-side expression incompatibilities with the Go SDK. Also fix
quoted CSS class keys in data-class expressions, harden session cookie
settings (named cookie, Secure flag), simplify SetupRoutes to not
return an error, and regenerate templ output.
Migrate from the via meta-framework to direct dependencies:
- chi for routing, templ for HTML templates, datastar for SSE/reactivity
- Feature-sliced architecture (features/{auth,lobby,c4game,snakegame}/)
- Shared layouts and components (features/common/)
- Handler factory pattern (HandleX(deps) http.HandlerFunc)
- Embedded NATS server (nats/), SCS sessions (sessions/), chi router wiring (router/)
- Move ChatMessage domain type from ui package to game package
- Remove old ui/ package (gomponents-based via/h views)
- Remove via dependency from go.mod entirely
