feat(catalog-config): mirror manifest v2 schema in validator + site

Phase D of v2.3 template configuration — closes the loop between the
Swift app and the catalog pipeline. Authors can now ship schemaful
bundles; the Python validator enforces the same invariants the Swift
installer does; the catalog site displays the schema so visitors see
what they'll need to configure before installing.

Python validator (tools/build-catalog.py):
- SUPPORTED_SCHEMA_VERSIONS accepts both 1 and 2 (v1 bundles are
  unchanged; v2 adds optional manifest.config).
- New _validate_config_schema function mirrors the Swift
  ProjectConfigService.validateSchema rules: unique keys, supported
  types, enum option presence + unique values, list itemType ==
  "string", secret-field cannot declare a default,
  modelRecommendation.preferred non-empty when present.
- _validate_contents_claim cross-checks contents.config (field count)
  against config.schema actual length — mismatch refused.
- TemplateRecord.to_catalog_entry exposes `config` in catalog.json so
  the site can render the schema.
- render_site copies each bundle's template.json to the detail dir as
  manifest.json (only when the manifest has a config block — keeps
  the served tree lean and makes "no manifest.json" a meaningful
  404 signal in the frontend).
- catalog.json's own schemaVersion stays at 1 (independent of per-
  template manifest schemaVersion).

Python tests (tools/test_build_catalog.py): 8 new cases in a new
ConfigSchemaValidationTests suite — accepts schemaful bundle, rejects
duplicate keys, rejects secret-with-default, rejects enum-without-
options, rejects unsupported field type, rejects contents.config
count mismatch, rejects unsupported list itemType, legacy v1
manifests pass unchanged. 24/24 Python tests total.

Site (site/widgets.js):
- New renderConfigSchema(container, config) — mirrors the display
  on the Scarf install preview. Renders each field as a <dt>/<dd>
  pair with type + required badges; enum shows choice labels; list
  fields show min/max bounds; string fields show pattern/length;
  secret fields get a "Stored in Keychain" reassurance. Optional
  modelRecommendation panel at the bottom with preferred + rationale
  + alternatives.
- The renderer is display-only — the site never collects values;
  that's the Scarf app's job.

template.html.tmpl adds a #config-schema <section>. The inline script
fetches manifest.json from the detail dir; on success hands the
config block to ScarfWidgets.renderConfigSchema; on 404 (schema-less
templates) silently leaves the section empty. CSS in styles.css
adds a config-schema panel matching the accent-green aesthetic.

24/24 Python + 50/50 Swift tests pass. site-status-checker still
renders correctly (schema-less; manifest.json isn't copied for it).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

site/template.html.tmpl

@@ -48,6 +48,10 @@
       <div id="dashboard-preview"></div>
     </section>
 
+    <section class="detail-config">
+      <div id="config-schema"></div>
+    </section>
+
     <section class="detail-readme">
       <h2>README</h2>
       <div id="readme-body"></div>
@@ -63,11 +67,14 @@
 
   <script src="../widgets.js"></script>
   <script>
-    // Fetch + render dashboard + README at page load. Both files live
-    // alongside index.html in this template's detail dir.
+    // Fetch + render dashboard + README + config schema at page load.
+    // Dashboard + README live next to index.html in this template's
+    // detail dir; the config schema comes from the sibling manifest.json
+    // that the build-catalog renderer also copies in.
     (async function () {
       const dashboardEl = document.getElementById("dashboard-preview");
       const readmeEl = document.getElementById("readme-body");
+      const configEl = document.getElementById("config-schema");
       try {
         const d = await fetch("dashboard.json").then(r => r.json());
         ScarfWidgets.renderDashboard(dashboardEl, d);
@@ -80,6 +87,17 @@
       } catch (e) {
         readmeEl.textContent = "Could not load README.";
       }
+      try {
+        // manifest.json may not exist for schema-less templates — that's
+        // fine, we just leave the config section empty.
+        const res = await fetch("manifest.json");
+        if (res.ok) {
+          const manifest = await res.json();
+          ScarfWidgets.renderConfigSchema(configEl, manifest.config);
+        }
+      } catch (e) {
+        // Silent — config-schema display is optional.
+      }
     })();
   </script>
 </body>