fix: force LF on *.txt so generated llms.txt stays clean on Windows

[Olamiaca]

Symptom

On Windows, git status in a gstack install permanently reports M gstack/llms.txt. Because /gstack-upgrade runs git stash before git reset --hard origin/main, every upgrade silently stashes this phantom change, accruing empty stashes and printing warning: in the working copy of 'gstack/llms.txt', LF will be replaced by CRLF the next time Git touches it.

Cause

.gitattributes already pins text eol=lf for every other generated/parsed text type — *.md, *.tmpl, *.yml, *.json, *.toml, *.ts, *.sh, setup, bin/* — and its own header comment says why:

Without this, Windows checkouts with core.autocrlf=true convert these to CRLF and break tests...

But there is no *.txt rule. gstack/llms.txt is regenerated as LF by ./setup's gen-llms-txt on every run, while the Git for Windows installer sets core.autocrlf=true at the system level (C:/Program Files/Git/etc/gitconfig). So the file falls through to the CRLF expectation and is flagged dirty forever.

Evidence

Both the committed blob and the worktree copy are pure LF (zero CR bytes), and git diff is empty — the file is phantom-modified, not content-modified:

$ git show HEAD:gstack/llms.txt | grep -c $'\r'   # 0
$ grep -c $'\r' gstack/llms.txt                   # 0
$ git diff gstack/llms.txt                        # (empty)
$ git status --porcelain                          #  M gstack/llms.txt

Only llms.txt trips it because ./setup rewrites the file each run, resetting its mtime and forcing git to re-evaluate it. Other .txt files keep a matching stat cache and are never re-examined.

Scope

*.txt matches exactly two tracked files:

• gstack/llms.txt — the target.
• make-pdf/test/fixtures/combined-gate.expected.txt — already pure LF and clean, so unaffected. LF is also correct here: it is compared against generated output, and a CRLF fixture vs LF output would fail.

No CI impact: on Linux runners autocrlf is off and files are already LF, so text eol=lf is a no-op there.

Verification

With the rule in place, git check-attr text eol -- gstack/llms.txt reports text: set / eol: lf, and rewriting the file with identical LF content (what ./setup does) leaves the worktree clean instead of dirty.

Deliberately omitted

No VERSION bump and no CHANGELOG entry — those belong to the maintainer's /ship release flow rather than a contributor's one-line fix.

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