refactor: rewrite build log as high-level capability summary

Replace raw per-commit feature name table with a capability areas table
(Core Pipeline, CI/CD, CLI, Git Hooks, etc.) derived from files touched.
Commit timeline moves to the main section with what/why/impact as prose,
gitmind tags demoted to a small footnote per entry.

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

Author: chanakyavasantha