fix: use table_header_custom for custom headers in subscription pages

The table_header() macro doesn't support caller() - it takes a columns list.
Using {% call table_header() %} caused a Jinja2 error:
  "macro 'table_header' was invoked with two values for the special caller argument"

Changes:
- Add table_header_custom() macro that supports caller() for custom headers
- Update subscriptions.html, subscription-tiers.html, billing-history.html
- Add TPL-008 architecture rule to detect this pattern
- Renumber TPL-009 (block names) and TPL-010 (Alpine vars)

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

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

.architecture-rules/frontend.yaml

@@ -381,6 +381,37 @@ template_rules:
       recommended_pattern: '<template x-if="items.length === 0">No items</template>'
 
   - id: "TPL-008"
+    name: "Use table_header_custom for custom headers, not table_header"
+    severity: "error"
+    description: |
+      When using {% call %} to create custom table headers with th_sortable
+      or custom <th> elements, you MUST use table_header_custom(), not table_header().
+
+      The table_header() macro takes a columns list and does NOT support caller().
+      Using {% call table_header() %} causes a Jinja2 error:
+        "macro 'table_header' was invoked with two values for the special caller argument"
+
+      WRONG (causes 500 error):
+        {% call table_header() %}
+            {{ th_sortable('name', 'Name', 'sortBy', 'sortOrder') }}
+            <th class="px-4 py-3">Actions</th>
+        {% endcall %}
+
+      RIGHT (supports caller):
+        {% call table_header_custom() %}
+            {{ th_sortable('name', 'Name', 'sortBy', 'sortOrder') }}
+            <th class="px-4 py-3">Actions</th>
+        {% endcall %}
+
+      OR for simple headers (list of column names):
+        {{ table_header(['Name', 'Email', 'Status', 'Actions']) }}
+    pattern:
+      file_pattern: "app/templates/**/*.html"
+      anti_patterns:
+        - "{%\\s*call\\s+table_header\\s*\\(\\s*\\)\\s*%}"
+      required_alternative: "table_header_custom"
+
+  - id: "TPL-009"
     name: "Use valid block names from base templates"
     severity: "error"
     description: |