fix(code-review): address PR review findings — split gating, story_key guard, HALT

- Split section 6 guard: story file status gated on spec_file only,
  sprint-status sync sub-gated on story_key separately
- Add conditional branch for manual choice in multi-story path so
  story_key is cleared when user declines a story selection
- Add HALT directive after Next steps menu to prevent LLM runaway

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/bmm-skills/4-implementation/bmad-code-review/steps/step-01-gather-context.md

@@ -25,7 +25,7 @@ story_key: '' # set at runtime when discovered from sprint status
    - **If a clear match is found:** Announce the detected mode (e.g., "Detected intent: review staged changes only") and proceed directly to constructing `{diff_output}` using the corresponding sub-case from instruction 3. Skip to instruction 4 (spec question).
    - **If no match from invocation text, check sprint tracking.** Look for a sprint status file (`*sprint-status*`) in `{implementation_artifacts}` or `{planning_artifacts}`. If found, scan for any story with status `review`. Handle as follows:
      - **Exactly one `review` story:** Set `{story_key}` to the story's key (e.g., `1-2-user-auth`). Suggest it: "I found story {{story-id}} in `review` status. Would you like to review its changes? [Y] Yes / [N] No, let me choose". If confirmed, use the story context to determine the diff source (branch name derived from story slug, or uncommitted changes). If declined, clear `{story_key}` and fall through to instruction 2.
-     - **Multiple `review` stories:** Present them as numbered options alongside a manual choice option. Wait for user selection. Set `{story_key}` to the selected story's key. Then use the selected story's context to determine the diff source as in the single-story case above, and proceed to instruction 3.
+     - **Multiple `review` stories:** Present them as numbered options alongside a manual choice option. Wait for user selection. If the user selects a story, set `{story_key}` to the selected story's key and use the selected story's context to determine the diff source as in the single-story case above, and proceed to instruction 3. If the user selects the manual choice, clear `{story_key}` and fall through to instruction 2.
    - **If no match and no sprint tracking:** Fall through to instruction 2.
 
 2. HALT. Ask the user: **What do you want to review?** Present these options:

src/bmm-skills/4-implementation/bmad-code-review/steps/step-04-present.md

@@ -85,7 +85,7 @@ If `{spec_file}` is **not** set, present only options 1 and 3 (omit option 2 —
 
 ### 6. Update story status and sync sprint tracking
 
-Skip this section if `{spec_file}` is not set or `{story_key}` is not set.
+Skip this section if `{spec_file}` is not set.
 
 #### Determine new status based on review outcome
 
@@ -96,6 +96,8 @@ Save the story file.
 
 #### Sync sprint-status.yaml
 
+If `{story_key}` is not set, skip this subsection and note that sprint status was not synced because no story key was available.
+
 If `{sprint_status}` file exists:
 
 1. Load the FULL `{sprint_status}` file.
@@ -123,3 +125,5 @@ Present the user with follow-up options:
 > 1. **Start the next story** — run `dev-story` to pick up the next `ready-for-dev` story
 > 2. **Re-run code review** — address findings and review again
 > 3. **Done** — end the workflow
+
+**HALT** — I am waiting for your choice. Do not proceed until the user selects an option.