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>

docs/api/openapi.yaml

@@ -5216,6 +5216,9 @@ components:
           type: string
           nullable: true
           description: Owning user ID for user-created templates; null for official presets
+        is_public:
+          type: boolean
+          description: Whether a user-created template is published to the public catalog
         created_at:
           type: string
           format: date-time
@@ -5251,6 +5254,9 @@ components:
           items:
             $ref: '#/components/schemas/TemplateVariable'
           description: Configurable variables exposed at deploy time
+        is_public:
+          type: boolean
+          description: Publish this template to the public catalog (visible anonymously)
 
     TemplateConfig:
       type: object