docs: clarify commit-based scope for branch comparisons

[danielsuguimoto]

Ticket

SKIPPED

Description

Updates command docs and shared components to clarify that branch comparisons should treat commits ahead of base as the authoritative scope of work, using file diffs only as supporting context. This ensures consistent behavior across PR creation, review, and ticket workflows.

Checklist

Command docs

• pr/create.md updated with commit-scope guidance
• review.md updated to reference commits ahead of base
• ticket/create.md updated with commit-scope guidance

Component templates

• change-summary.md updated to prioritize commits over branch names
• changes-summary.md updated with commit validation rule
• summarize-changes.md updated to scope from commits only

Generated output

• OpenCode artifacts in packages/opencode/.opencode/ regenerated and synced

Validation

• Verify that all modified command docs reference commit-based scope
• Confirm that generated .opencode/ files match source changes
• Check that no raw branch comparison strings are used as primary scope descriptions