Standardize backend/tools file headers

Give all three tools the same header shape: shebang, summary docstring, a
short detail paragraph, and a "Run from the backend directory:" command
block. Adds docstrings to generate_supported_platforms.py and
xml_diagnostics.py, which previously had none.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/tools/generate_supported_platforms.py

@@ -1,4 +1,15 @@
-# uv run python -m tools.generate_supported_platforms
+#!/usr/bin/env python3
+"""Print the supported-platforms table (Markdown) for the docs.
+
+Walks every UniversalPlatformSlug, collects each metadata provider's
+platform mapping, and emits a Markdown table (with provider link icons) to
+stdout for pasting into the documentation.
+
+Run from the backend directory:
+
+    uv run python -m tools.generate_supported_platforms
+"""
+
 from typing import TypedDict
 from urllib.parse import quote
 

backend/tools/xml_diagnostics.py

@@ -1,3 +1,15 @@
+#!/usr/bin/env python3
+"""Diagnose a malformed XML file: bad encoding, invalid chars, parse errors.
+
+Reads the file in chunks to surface UTF-8 issues, then runs SAX and
+ElementTree parsing to report the location of structural errors, with a few
+lines of context around each one.
+
+Run from the backend directory:
+
+    uv run tools/xml_diagnostics.py <xml_file>
+"""
+
 import sys
 from xml.sax.handler import ContentHandler  # nosec
 
@@ -79,6 +91,6 @@ def diagnose_xml(filename):
 
 if __name__ == "__main__":
     if len(sys.argv) != 2:
-        print("Usage: python script.py <xml_file>")
+        print("Usage: uv run tools/xml_diagnostics.py <xml_file>")
         sys.exit(1)
     diagnose_xml(sys.argv[1])