Phase 0: project scaffold

- Go module + chi server with embedded SPA serving and /api/health
- internal/config env loader (local-dev defaults; auth/copyleaks deferred)
- React 19 + Vite 6 + Tailwind v4 frontend with full Petal design tokens
- Frontend embedded into the binary via web/embed.go (go:embed all:dist)
- README dev workflow, .env.example, BUILD_PLAN progress tracker
- Verified end-to-end: binary serves health, embedded SPA, and SPA fallback

cmd/server/main.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"errors"
+	"io/fs"
+	"log"
+	"net/http"
+	"strings"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+
+	"gitea.parodia.dev/drwily/petal/internal/config"
+	"gitea.parodia.dev/drwily/petal/web"
+)
+
+func main() {
+	cfg := config.Load()
+
+	r := chi.NewRouter()
+	r.Use(middleware.RequestID)
+	r.Use(middleware.RealIP)
+	r.Use(middleware.Logger)
+	r.Use(middleware.Recoverer)
+
+	r.Route("/api", func(api chi.Router) {
+		api.Get("/health", func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"status":"ok"}`))
+		})
+	})
+
+	// Everything else: serve the embedded SPA (with index.html fallback for client routing).
+	r.NotFound(spaHandler())
+
+	addr := ":" + cfg.Port
+	log.Printf("petal listening on %s (LLM backend=%s)", addr, cfg.LLMBackend)
+	if err := http.ListenAndServe(addr, r); err != nil {
+		log.Fatalf("server error: %v", err)
+	}
+}
+
+// spaHandler serves the embedded web/dist as a single-page app: static files
+// when they exist, falling back to index.html for unknown paths. If the
+// frontend hasn't been built yet, it returns a friendly dev hint instead.
+func spaHandler() http.HandlerFunc {
+	sub, err := fs.Sub(web.DistFS, "dist")
+	if err != nil {
+		log.Fatalf("embed sub: %v", err)
+	}
+
+	if _, err := fs.Stat(sub, "index.html"); errors.Is(err, fs.ErrNotExist) {
+		return func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+			w.WriteHeader(http.StatusOK)
+			_, _ = w.Write([]byte("Petal backend is running, but the frontend isn't built yet.\n" +
+				"Run `npm run build` in web/, or use `npm run dev` for the dev server on :5173.\n"))
+		}
+	}
+
+	fileServer := http.FileServer(http.FS(sub))
+	return func(w http.ResponseWriter, req *http.Request) {
+		p := strings.TrimPrefix(req.URL.Path, "/")
+		if p == "" {
+			p = "index.html"
+		}
+		if _, err := fs.Stat(sub, p); errors.Is(err, fs.ErrNotExist) {
+			// Unknown path → let the SPA router handle it.
+			req2 := new(http.Request)
+			*req2 = *req
+			req2.URL.Path = "/"
+			fileServer.ServeHTTP(w, req2)
+			return
+		}
+		fileServer.ServeHTTP(w, req)
+	}
+}