refactor: replace via framework with chi + templ + datastar

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

features/lobby/handlers.go

@@ -0,0 +1,168 @@
+package lobby
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"github.com/ryanhamamura/c4/db/repository"
+	lobbycomponents "github.com/ryanhamamura/c4/features/lobby/components"
+	"github.com/ryanhamamura/c4/features/lobby/pages"
+	"github.com/ryanhamamura/c4/game"
+	"github.com/ryanhamamura/c4/snake"
+
+	"github.com/alexedwards/scs/v2"
+	"github.com/go-chi/chi/v5"
+	"github.com/starfederation/datastar-go/datastar"
+)
+
+// HandleLobbyPage renders the main lobby page with active games for logged-in users.
+func HandleLobbyPage(queries *repository.Queries, sessions *scs.SessionManager, snakeStore *snake.SnakeStore) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		userID := sessions.GetString(r.Context(), "user_id")
+		username := sessions.GetString(r.Context(), "username")
+		isLoggedIn := userID != ""
+
+		var userGames []lobbycomponents.GameListItem
+		if isLoggedIn {
+			ctx := context.Background()
+			games, err := queries.GetUserActiveGames(ctx, sql.NullString{String: userID, Valid: true})
+			if err == nil {
+				for _, g := range games {
+					isMyTurn := g.Status == 1 && g.CurrentTurn == g.MyColor
+					userGames = append(userGames, lobbycomponents.GameListItem{
+						ID:           g.ID,
+						Status:       int(g.Status),
+						OpponentName: g.OpponentNickname.String,
+						IsMyTurn:     isMyTurn,
+						LastPlayed:   g.UpdatedAt.Time,
+					})
+				}
+			}
+		}
+
+		var activeSnakeGames []pages.SnakeGameListItem
+		for _, g := range snakeStore.ActiveGames() {
+			statusLabel := "Waiting"
+			if g.Status == snake.StatusCountdown {
+				statusLabel = "Starting soon"
+			}
+			activeSnakeGames = append(activeSnakeGames, pages.SnakeGameListItem{
+				ID:          g.ID,
+				Width:       g.State.Width,
+				Height:      g.State.Height,
+				PlayerCount: g.PlayerCount(),
+				StatusLabel: statusLabel,
+			})
+		}
+
+		data := pages.LobbyData{
+			IsLoggedIn:       isLoggedIn,
+			Username:         username,
+			UserGames:        userGames,
+			ActiveSnakeGames: activeSnakeGames,
+		}
+
+		if err := pages.LobbyPage(data).Render(r.Context(), w); err != nil {
+			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+		}
+	}
+}
+
+// HandleCreateGame reads the nickname signal, creates a connect4 game, and redirects via SSE.
+func HandleCreateGame(store *game.GameStore, sessions *scs.SessionManager) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		type Signals struct {
+			Nickname string `json:"nickname"`
+		}
+		signals := &Signals{}
+		if err := datastar.ReadSignals(r, signals); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		if signals.Nickname == "" {
+			return
+		}
+
+		sessions.Put(r.Context(), "nickname", signals.Nickname)
+
+		gi := store.Create()
+		sse := datastar.NewSSE(w, r)
+		sse.ExecuteScript(fmt.Sprintf("window.location.href='/game/%s'", gi.ID()))
+	}
+}
+
+// HandleDeleteGame deletes a connect4 game and redirects to the lobby.
+func HandleDeleteGame(store *game.GameStore, sessions *scs.SessionManager) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		gameID := chi.URLParam(r, "id")
+		if gameID == "" {
+			http.Error(w, "missing game id", http.StatusBadRequest)
+			return
+		}
+
+		store.Delete(gameID)
+
+		sse := datastar.NewSSE(w, r)
+		sse.ExecuteScript("window.location.href='/'")
+	}
+}
+
+// HandleCreateSnakeGame reads nickname, grid preset, speed, and mode from the request,
+// creates a snake game, and redirects via SSE.
+func HandleCreateSnakeGame(snakeStore *snake.SnakeStore, sessions *scs.SessionManager) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		type Signals struct {
+			Nickname      string `json:"nickname"`
+			SelectedSpeed int    `json:"selectedSpeed"`
+		}
+		signals := &Signals{}
+		if err := datastar.ReadSignals(r, signals); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		if signals.Nickname == "" {
+			return
+		}
+
+		sessions.Put(r.Context(), "nickname", signals.Nickname)
+
+		mode := snake.ModeMultiplayer
+		if r.URL.Query().Get("mode") == "solo" {
+			mode = snake.ModeSinglePlayer
+		}
+
+		presetIdx, _ := strconv.Atoi(r.URL.Query().Get("preset"))
+		if presetIdx < 0 || presetIdx >= len(snake.GridPresets) {
+			presetIdx = 0
+		}
+		preset := snake.GridPresets[presetIdx]
+
+		speed := snake.DefaultSpeed
+		if signals.SelectedSpeed >= 0 && signals.SelectedSpeed < len(snake.SpeedPresets) {
+			speed = snake.SpeedPresets[signals.SelectedSpeed].Speed
+		}
+
+		si := snakeStore.Create(preset.Width, preset.Height, mode, speed)
+
+		sse := datastar.NewSSE(w, r)
+		sse.ExecuteScript(fmt.Sprintf("window.location.href='/snake/%s'", si.ID()))
+	}
+}
+
+// HandleLogout clears the session and redirects to the lobby.
+func HandleLogout(sessions *scs.SessionManager) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if err := sessions.Destroy(r.Context()); err != nil {
+			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+			return
+		}
+
+		sse := datastar.NewSSE(w, r)
+		sse.ExecuteScript("window.location.href='/'")
+	}
+}