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/frontend/src/generated/api-types.ts

@@ -7806,6 +7806,8 @@ export interface components {
             is_official?: boolean;
             /** @description Owning user ID for user-created templates; null for official presets */
             owner_id?: string | null;
+            /** @description Whether a user-created template is published to the public catalog */
+            is_public?: boolean;
             /**
              * Format: date-time
              * @description Creation timestamp
@@ -7830,6 +7832,8 @@ export interface components {
             config: Record<string, never>;
             /** @description Configurable variables exposed at deploy time */
             variables?: components["schemas"]["TemplateVariable"][];
+            /** @description Publish this template to the public catalog (visible anonymously) */
+            is_public?: boolean;
         };
         TemplateConfig: {
             /** @description Service type for created service */