refactor: both tools import the same fragments; scope code comments by path

Codex reads ~/.codex/AGENTS.md, not ~/.agents/AGENTS.md, so the file
generated there last commit was inert. Both tools support @path imports,
which removes the generate-and-drift step entirely.

code-comments.md moves to ~/.claude/rules/ with paths frontmatter, so its
24 lines load only when a source file is read.

hooks/comment-lint.py

@@ -2,7 +2,7 @@
 """PostToolUse nudge for code comments: Write / Edit / MultiEdit.
 
 Lints ONLY the newly-added text against the "Code comments" contract in
-~/.claude/writing.md, so legacy files are not re-flagged on every touch.
+~/.claude/rules/code-comments.md, so legacy files are not re-flagged on every touch.
 
 Exit 0 = silent. Exit 2 = stderr goes back to Claude as feedback; the edit is
 already applied, so this is a revise-it nudge, not a block.
@@ -157,7 +157,7 @@ def main():
     name = os.path.basename(path)
 
     if problems:
-        lines = [f"Comment contract (~/.claude/writing.md) — {name}:", ""]
+        lines = [f"Comment contract (~/.claude/rules/code-comments.md) — {name}:", ""]
         lines += [f"  - {p}" for p in problems + notes]
         lines += ["", "Trim what you just wrote, or say why it stays."]
         print("\n".join(lines), file=sys.stderr)