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>

scripts/validate_architecture.py

@@ -1306,6 +1306,38 @@ class ArchitectureValidator:
                     )
                     break  # Only report once per line
 
+    def _check_page_header_macro_api(
+        self, file_path: Path, content: str, lines: list[str]
+    ):
+        """
+        TPL-015: Check for old page_header macro API.
+
+        The page_header macro does not accept a buttons=[] parameter.
+        Use action_label/action_onclick for single button, or page_header_flex for multiple.
+
+        OLD (deprecated): {{ page_header('Title', buttons=[...]) }}
+        NEW (correct):    {{ page_header('Title', action_label='Add', action_onclick='...') }}
+        """
+        # Skip the macro definition file
+        if "shared/macros/headers.html" in str(file_path):
+            return
+
+        if "noqa: tpl-015" in content.lower():
+            return
+
+        for i, line in enumerate(lines, 1):
+            if re.search(r"page_header\s*\([^)]*buttons\s*=", line):
+                self._add_violation(
+                    rule_id="TPL-015",
+                    rule_name="Use correct page_header macro API",
+                    severity=Severity.ERROR,
+                    file_path=file_path,
+                    line_number=i,
+                    message="page_header does not accept 'buttons' parameter",
+                    context=line.strip()[:80],
+                    suggestion="Use action_label/action_onclick, or page_header_flex with {% call %}",
+                )
+
     def _check_alpine_template_vars(
         self, file_path: Path, content: str, lines: list[str], js_content: str
     ):
@@ -3286,6 +3318,9 @@ class ArchitectureValidator:
             # TPL-014: Check for old modal_simple macro API
             self._check_modal_simple_macro_api(file_path, content, lines)
 
+            # TPL-015: Check for old page_header macro API
+            self._check_page_header_macro_api(file_path, content, lines)
+
             # Skip base/partials for TPL-001 check
             if is_base_or_partial:
                 continue