feat: public template catalog + Vercel git integration

Backend: service_templates.is_public lets owners publish user templates to
the anonymous catalog (GET /api/v1/templates), mirroring Railway's
marketplace publish flow. Migration, sqlc queries, visibility rules, and
openapi.yaml updated; types regenerated.

App: template editor gains a "List in the public catalog" checkbox;
Public badge on catalog cards and detail view.

Site: new templates.html catalog page - search, category filters, Official
vs Community badges, detail modal with variables and copyable import JSON.
Fetches the live catalog from a reachable instance (?api= or localStorage
override) and falls back to templates.json, generated from SeedTemplates
via cmd/dumptemplates. Shared styles extracted to style.css.

Vercel: project connected to GitHub repo with rootDirectory=site;
.vercelignore limits CLI uploads to site/ so `vercel deploy --prod` from
repo root matches git builds.

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/cmd/dumptemplates/main.go

@@ -0,0 +1,24 @@
+// dumptemplates prints the seeded official template catalog as JSON in the same
+// shape as GET /api/v1/templates. The landing site (site/templates.json) uses it
+// as the offline fallback catalog: `go run ./cmd/dumptemplates > ../../site/templates.json`.
+package main
+
+import (
+	"containr/internal/api"
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+func main() {
+	out := struct {
+		Templates []api.ServiceTemplate `json:"templates"`
+	}{Templates: api.SeedTemplates()}
+
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(out); err != nil {
+		fmt.Fprintln(os.Stderr, "encode:", err)
+		os.Exit(1)
+	}
+}