DOCFIX-143: repo_lint.py no longer relies on git to clean up its own CRLF ...

The --record-clientdocs-sweep/--record-guide-skill-coupling writers used
write_text(), which translates \n to the platform newline (CRLF on Windows)
before writing. .gitattributes' eol=lf silently cleaned this up at every
`git add`, so no CRLF ever reached a commit, but the script was depending on
git to fix its own sloppy output -- flagged during the DOCFIX-141 commit.
Both writers now build the string, .encode("ascii") it, and write_bytes() it
directly. ascii (not utf-8) deliberately: this repo's own rule is ASCII-only,
so a future non-ASCII path/hash now raises loudly here instead of writing
content L1 would fail on anyway.

Verified live: re-ran --record-clientdocs-sweep, byte-inspected the receipt
(0 CR, was 41/41 CR/LF before). tests/repo-lint harness 34/34 unchanged.
repo-lint 0 fail / 1 documented warn.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A