fix(#4665): route --fix past the empty-scope exit (#4810)

* test(#4665): add failing-first contract coverage for the --fix empty-scope recovery

* fix(#4665): route --fix past the empty-scope exit

check_empty_scope exited the entire workflow whenever REVIEW_FILES was
empty — before dispatch-fix — so with #3661's incremental scoping, a phase
whose only post-review changes were planning artifacts could never run
--fix against its standing REVIEW.md findings, and the skip output did not
even mention the flag.

The skip is now a self-contained guarded fence (explicit REVIEW_FILES
emptiness check): it fires only when --fix is absent OR the phase's
REVIEW.md does not exist. Otherwise the workflow proceeds directly to
dispatch-fix, which delegates to code-review-fix.md — the canonical fix
implementation that already documents handling an existing REVIEW.md —
while the fresh-review steps (structural pre-pass, reviewer lanes,
spawn_reviewer, commit_review) are skipped: nothing new to review, nothing
to commit. dispatch-fix.md's route docstring is synced.

Emitted-Drift-Ack-Growth: code-review.md — check_empty_scope gains the --fix recovery branch (#4665)

* docs(#4665): backfill changeset PR number

---------

Co-authored-by: sim <sim@local>

.changeset/proud-elks-fly.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4810
+---
+**`/gsd-code-review --fix` now works on an existing REVIEW.md even when no source files changed** — incremental scoping (#3661) narrowed the review file set to empty for phases whose only post-review changes were planning artifacts, and the empty-scope check exited the whole workflow before the fix step, so standing findings could never be addressed. With `--fix` and an existing REVIEW.md, the empty scope now routes straight to the fix workflow instead of skipping. (#4665)