Quickstart: Fix Merge Target Branch Resolution

Problem

spec-kitty merge --feature <slug> ignores meta.json target_branch and defaults to repo primary branch. Features targeting 2.x get merged into main.

Fix Summary

3 changes:

1. merge.py lines 721-724: When --feature is provided and --target is not, call get_feature_target_branch(repo_root, feature) instead of resolve_primary_branch(repo_root).

2. merge.md template: Align frontmatter and body to the single canonical API spec-kitty merge --feature <slug>. Remove all references to spec-kitty agent feature merge from templates.

3. Regression tests: 7 test cases covering 2.x target, main target, missing meta.json, explicit override, nonexistent branch error, no-feature backward compat, malformed meta.json.

Verification

# After fix, this should show target_branch: "2.x" for a 2.x-targeting feature:
spec-kitty merge --feature 049-fix-merge-target-resolution --dry-run --json | python -m json.tool | grep target_branch

# Run regression tests:
python -m pytest tests/specify_cli/cli/commands/test_merge_target_resolution.py -v

Key Files

FileChange
src/specify_cli/cli/commands/merge.pyFix target resolution (lines 721-724)
src/specify_cli/missions/software-dev/command-templates/merge.mdAlign template to canonical spec-kitty merge path
tests/specify_cli/cli/commands/test_merge_target_resolution.pyNew regression tests
src/specify_cli/core/feature_detection.pyUnchanged (reused)