showcase: activity check uses all-branch last-commit date to avoid false inactivity

Problem: projects with active development on a non-default branch (e.g. all
recent work on 'master' while the workdir HEAD is on 'screenshots') were
being greyed out in the rank-history SVG despite recent commits.

Fix:
- Add LastActivityDate string to RepoMetadata, computed with
  'git log --all -1 --pretty=format:%ai' (all local branches, no fetch).
  Code stats (AvgCommitAge, CommitCount, LOC, score) remain HEAD-only per
  the configured-branch rules.
- SVG inactivity check uses LastActivityDate (falling back to LastCommitDate
  if the field is absent in older cache entries).
- getLastActivityDate() added to metadata.go alongside getLastCommitDate().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions