fix(tests): apply user edits when creating test from template

The form captured name/description/platform/procedure/tool edits but
never sent them — the created test always used the raw template values.

- TestTemplateInstantiate schema: add optional override fields
  (name, description, platform, procedure_text, tool_used)
- create_test_from_template service: accept *_override kwargs;
  use override value when provided, fall back to template value
- Router: pass all override fields from payload to service
- Frontend API createTestFromTemplate: accept overrides object, spread into body
- TestFromTemplateForm: pass all form state values as overrides

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/TestFromTemplateForm.tsx

@@ -68,7 +68,14 @@ export default function TestFromTemplateForm({
   // ── Submit ─────────────────────────────────────────────────────
 
   const createMutation = useMutation({
-    mutationFn: () => createTestFromTemplate(templateId, technique),
+    mutationFn: () =>
+      createTestFromTemplate(templateId, technique, {
+        name: name.trim() || undefined,
+        description: description.trim() || undefined,
+        platform: platform.trim() || undefined,
+        procedure_text: procedureText.trim() || undefined,
+        tool_used: toolUsed.trim() || undefined,
+      }),
     onSuccess: (test) => {
       navigate(`/tests/${test.id}`);
     },