feat: add architecture rule TPL-015 for page_header macro API

Detects deprecated buttons=[] parameter usage in page_header macro.

Correct API:
- Single button: action_label, action_icon, action_onclick
- Multiple buttons: use page_header_flex with {% call %}

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.architecture-rules/frontend.yaml

@@ -561,6 +561,39 @@ template_rules:
       exceptions:
         - "shared/macros/pagination.html"
 
+  - id: "TPL-015"
+    name: "Use correct page_header macro API"
+    severity: "error"
+    description: |
+      The page_header macro does not accept a buttons=[] parameter.
+      Use action_label/action_onclick for a single action button,
+      or use page_header_flex with {% call %} for multiple buttons.
+
+      OLD (deprecated - will break):
+        {{ page_header('Title', buttons=[
+            {'text': 'Add', 'icon': 'plus', 'click': 'doSomething()'}
+        ]) }}
+
+      NEW (single action button):
+        {{ page_header('Title', action_label='Add', action_icon='plus', action_onclick='doSomething()') }}
+
+      NEW (multiple buttons - use page_header_flex):
+        {% call page_header_flex(title='Title') %}
+        <button @click="action1()">Button 1</button>
+        <button @click="action2()">Button 2</button>
+        {% endcall %}
+
+      Parameters for page_header:
+        - title, subtitle
+        - action_label, action_url, action_icon, action_onclick
+        - back_url, back_label
+    pattern:
+      file_pattern: "app/templates/**/*.html"
+      anti_patterns:
+        - "page_header\\s*\\([^)]*buttons\\s*="
+      exceptions:
+        - "shared/macros/headers.html"
+
   - id: "TPL-014"
     name: "Use new modal_simple macro API with call block"
     severity: "error"