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>

app/templates/admin/subscriptions.html

@@ -2,7 +2,7 @@
 {% extends "admin/base.html" %}
 {% from 'shared/macros/alerts.html' import alert_dynamic, error_state %}
 {% from 'shared/macros/headers.html' import page_header_refresh %}
-{% from 'shared/macros/tables.html' import table_wrapper, table_header, th_sortable %}
+{% from 'shared/macros/tables.html' import table_wrapper, table_header_custom, th_sortable %}
 {% from 'shared/macros/pagination.html' import pagination_full %}
 
 {% block title %}Vendor Subscriptions{% endblock %}
@@ -139,7 +139,7 @@
 <!-- Subscriptions Table -->
 {% call table_wrapper() %}
     <table class="w-full whitespace-nowrap">
-        {% call table_header() %}
+        {% call table_header_custom() %}
             {{ th_sortable('vendor_name', 'Vendor', 'sortBy', 'sortOrder') }}
             {{ th_sortable('tier', 'Tier', 'sortBy', 'sortOrder') }}
             {{ th_sortable('status', 'Status', 'sortBy', 'sortOrder') }}