fix(code-review): address review findings in step-01 intent cascade

- Set {spec_file} immediately in Tier 1 when spec provided
- Add staged/uncommitted handlers to instruction 3 dispatch table
- Replace undefined {branch}/{sha} placeholders with angle brackets
- Fix {story_key} vs {{story-id}} placeholder mismatch
- Correct "wants reviewed" grammar to "wants to be reviewed"

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

@@ -21,21 +21,21 @@ story_key: '' # set at runtime when discovered from sprint status
    Did the user pass a PR, commit SHA, branch, spec file, or diff source this message?
    - PR reference → resolve to branch/commit via `gh pr view`. If resolution fails, ask for a SHA or branch.
    - Commit or branch → use directly.
-   - Spec file → check its frontmatter for `baseline_commit`. If found, use as diff baseline. If not found, note the spec for instruction 4 and continue the cascade (a spec alone does not identify a diff source).
+   - Spec file → set `{spec_file}` to the provided path. Check its frontmatter for `baseline_commit`. If found, use as diff baseline. If not found, continue the cascade (a spec alone does not identify a diff source).
    - Also scan the argument for diff-mode keywords that narrow the scope:
      - "staged" / "staged changes" → Staged changes only
      - "uncommitted" / "working tree" / "all changes" → Uncommitted changes (staged + unstaged)
-     - "branch diff" / "vs main" / "against main" / "compared to {branch}" → Branch diff (extract base branch if mentioned)
+     - "branch diff" / "vs main" / "against main" / "compared to <branch>" → Branch diff (extract base branch if mentioned)
-     - "commit range" / "last N commits" / "{sha}..{sha}" → Specific commit range
+     - "commit range" / "last N commits" / "<from-sha>..<to-sha>" → Specific commit range
      - "this diff" / "provided diff" / "paste" → User-provided diff (do not match bare "diff" — it appears in other modes)
    - When multiple keywords match, prefer the most specific (e.g., "branch diff" over bare "diff").
 
    **Tier 2 — Recent conversation.**
-   Do the last few messages reveal what the user wants reviewed? Look for spec paths, commit refs, branches, PRs, or descriptions of a change. Apply the same diff-mode keyword scan and routing as Tier 1.
+   Do the last few messages reveal what the user wants to be reviewed? Look for spec paths, commit refs, branches, PRs, or descriptions of a change. Apply the same diff-mode keyword scan and routing as Tier 1.
 
    **Tier 3 — Sprint tracking.**
    Look for a sprint status file (`*sprint-status*`) in `{implementation_artifacts}` or `{planning_artifacts}`. If found, scan for stories with status `review`:
-   - **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.
+   - **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.
    - **Multiple `review` stories:** Present them as numbered options alongside a manual choice option. Wait for user selection. If a story is selected, set `{story_key}` and use its context to determine the diff source. If manual choice is selected, clear `{story_key}` and fall through.
    - **None:** Fall through.
 
@@ -55,13 +55,17 @@ story_key: '' # set at runtime when discovered from sprint status
    - **Provided diff or file list** (user pastes or provides a path)
 
 3. Construct `{diff_output}` from the chosen source.
+   - For **staged changes only**: run `git diff --cached`.
+   - For **uncommitted changes** (staged + unstaged): run `git diff HEAD`.
    - For **branch diff**: verify the base branch exists before running `git diff`. If it does not exist, HALT and ask the user for a valid branch.
    - For **commit range**: verify the range resolves. If it does not, HALT and ask the user for a valid range.
    - For **provided diff**: validate the content is non-empty and parseable as a unified diff. If it is not parseable, HALT and ask the user to provide a valid diff.
    - For **file list**: validate each path exists in the working tree. Construct `{diff_output}` by running `git diff HEAD -- <path1> <path2> ...`. If any paths are untracked (new files not yet staged), use `git diff --no-index /dev/null <path>` to include them. If the diff is empty (files have no uncommitted changes and are not untracked), ask the user whether to review the full file contents or to specify a different baseline.
    - After constructing `{diff_output}`, verify it is non-empty regardless of source type. If empty, HALT and tell the user there is nothing to review.
 
-4. Ask the user: **Is there a spec or story file that provides context for these changes?**
+4. **Set the spec context.**
+   - If `{spec_file}` is already set (from Tier 1 or Tier 2): verify the file exists and is readable, then set `{review_mode}` = `"full"`.
+   - Otherwise, ask the user: **Is there a spec or story file that provides context for these changes?**
      - If yes: set `{spec_file}` to the path provided, verify the file exists and is readable, then set `{review_mode}` = `"full"`.
      - If no: set `{review_mode}` = `"no-spec"`.