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.

claude-md/code-comments.md

@@ -0,0 +1,24 @@
+---
+paths:
+  - "**/*.{ts,tsx,js,jsx,mjs,cjs,py,rs,go,sol,sh,bash,zsh,c,h,cc,cpp,hpp,java,kt,rb,lua,zig,nix,swift,php,cs,ex}"
+---
+
+## Code comments
+
+Budget: 1-3 lines. Write one only when an agent with the repo and thirty
+seconds of grep would still get it wrong. That means one of:
+
+- a landmine no test catches
+- a fact not in the repo (deployed bytecode, chain quirk, library bug)
+- a unit or epoch the type cannot carry (wei, ms, 18-dp)
+- a MUST or MUST NOT a caller can break
+
+Good:
+
+> `// MUST read lastGoodPrice before fetchPrice — same eth_call state.`
+
+Everything else: delete. Design rationale and rejected alternatives go in
+`docs/`; leave a path. History is in git. No emphasis; ALL-CAPS only for
+MUST / NEVER.
+
+Deleting a comment is cheap and reversible. When unsure, delete.