CI: fail the build on any file over 250 lines

Requirement 4 of "make it permanent": the pre-commit hook only ever sees the
files in a commit, so it cannot catch a violation that arrives by a path the
hook never ran on — a merge, a push from a machine without hooks installed, a
rebase that resurrects a file. This runs `check_file_length.sh --all` over the
whole tree on every push and PR to main.

Deliberately no `paths:` filter, unlike the other ten workflows: the cap
applies to every file in the repo, so scoping this job to a subdirectory is
the one change that would reintroduce exactly what it exists to catch.

Added last, because until the final doc split it would have failed on push.
Verified against a clean checkout of HEAD in a throwaway worktree — the exact
command the job runs exits 0 — and the commit gate re-tested in both
directions after file_length's own internals were refactored: a staged
261-line file fails (exit 1, no commit object), a 200-line one commits.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CFSGeWxHPY5rHUGrPqhcmG

.github/workflows/file-length.yml

@@ -0,0 +1,34 @@
+name: file length
+
+# The 250-line cap, enforced on push as well as in pre-commit
+# (refactor_claude_todo.md, "make it permanent").
+#
+# Unlike the pre-commit hook, which only sees the files in a commit, this runs
+# over the whole tree: the hook keeps a violation from being *introduced*, and
+# this keeps one from surviving a path the hook never saw (a merge, a push
+# from a machine without hooks installed, a rebase that resurrects a file).
+#
+# No paths filter on purpose. The cap applies to every file in the repo, so
+# scoping this job to a subdirectory would be the one way to reintroduce the
+# problem it exists to catch.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  file-length:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Every file is at most 250 lines
+        run: bash scripts/check_file_length.sh --all