fix(lefthook): remove duplicate git-lfs pre-push command

Lefthook v2 runs `git lfs pre-push` internally for pre-push hooks (per
docs/usage/features/git-lfs.md; confirmed in internal/run/controller/
lfs.go where the internal handler invokes `git lfs pre-push <remote>
<url>` with a buffered `cachedStdin`). Our manual `git-lfs:` command
in lefthook.yml was a second invocation against the same remote; the
duplicate is directly visible in `LEFTHOOK_VERBOSE=1` output as
`[git-lfs] executing hook` (internal) followed by `[lefthook] run:
git lfs pre-push` (manual).

The previous fix attempt (piped: true, commit 1b06804) was based on a
wrong understanding of `piped`'s semantics — `piped` controls
fail-fast behavior, not stdin routing or sequencing. Default lefthook
behavior is already sequential per docs/configuration/parallel.md.
That "fix" was placebo; incident 2 (F2 push, zero LFS objects, commit
99eedb6) proved it.

Phase A investigation: documentary + source confirmation that lefthook
owns the LFS pre-push call. Phase B sandbox test against a filesystem
remote confirmed the duplicate execution in logs but did NOT reproduce
the production hang — likely because the duplicate manual call against
a local remote has no LFS server to interact with. A network-y remote
(Gitea over SSH/HTTPS) appears to be part of the trigger. Two
mechanisms remain plausible (H1: PTY-stdin without EOF in
`while read` loop per docs/configuration/use_stdin.md; H4: server-side
LFS interaction on the duplicate call). Both are eliminated by the
same fix: remove the manual command. LFS uploads continue to work via
lefthook's internal handler (verified in sandbox post-fix).

Regression coverage: scripts/test-lefthook-pre-push.sh asserts exactly
one internal LFS invocation, zero manual ones, and `Uploading LFS
objects: 100%` present, against a disposable sandbox.

See dev-docs/ADR-LEFTHOOK-LFS-INTEGRATION.md for full context, both
misconceptions to prevent regression, and the alternative-scenarios
playbook if Phase E ever regresses.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

lefthook.yml

@@ -17,10 +17,11 @@ post-commit:
       run: bash .githooks/post-commit
 
 pre-push:
-  # piped: true forces serial execution. Both sync-check and git-lfs
-  # read from stdin (git pipes the push refspec to pre-push hooks);
-  # default parallel execution deadlocks with two stdin readers.
-  piped: true
+  # LFS is handled by lefthook's built-in pre-push LFS hook (see
+  # docs/usage/features/git-lfs.md). Do NOT add a manual `git lfs
+  # pre-push` command here — it duplicates the internal call and
+  # historically caused the pre-push to hang. Background and
+  # mechanism: dev-docs/ADR-LEFTHOOK-LFS-INTEGRATION.md.
   commands:
     sync-check:
       run: bash .githooks/pre-push
@@ -33,10 +34,3 @@ pre-push:
       # behaviour. (Pushing with zero new commits would be skipped
       # under lefthook but is a no-op for the sync-staleness warning
       # anyway, so behaviour stays effectively 1:1.)
-    git-lfs:
-      # `git lfs install --skip-repo` only sets up global clean/smudge
-      # filters — it does NOT install the per-repo pre-push hook
-      # (which would conflict with lefthook). We delegate the LFS
-      # upload step here so screenshot baselines tracked via LFS get
-      # pushed alongside their commits.
-      run: git lfs pre-push {1} {2}