test(10.1-04): cover the Phase 10.1 extension point Go code

- acme fixture plugin under modules/cabana/testdata/extension (gadgets
  controller, header and form partials, lookup widget, JS and CSS)
- TestPhase101FormExtensionSchema, TestPhase101PartialSchema and
  TestPhase101Toolbar: every widget, partial and toolbar boot rule
- TestPhase101PartialSanitizer: tag, attribute and URL allowlist, escaping,
  per-request trans, size/node/depth caps and the view-model guard
- TestPhase101Assets: exact-key asset hits, revalidation, SPA fall-through,
  boot path checks and ?v= schema URLs
- TestPhase101Actions (PostgreSQL): scoping, fill filter, strict body,
  action permission, error mapping, CSRF header, toolbar and partial routes
- TestPhase101BoardwalkExports: ContentType and SetSecurityHeaders

modules/cabana/testdata/extension/models/gadget/fields.yaml

@@ -0,0 +1,23 @@
+fields:
+    name:
+        label: acme.demo::lang.gadgets.name
+        type: text
+        span: left
+    active:
+        label: acme.demo::lang.gadgets.active
+        type: switch
+        span: right
+    group:
+        label: acme.demo::lang.gadgets.group
+        type: relation
+        nameFrom: title
+    lookup:
+        label: acme.demo::lang.gadgets.lookup
+        type: widget
+        widget: acme-demo-lookup
+        action: lookup
+        fill: [name, active]
+    summary:
+        label: acme.demo::lang.gadgets.summary
+        type: partial
+        path: summary