chore: add automated git commit/push workflow and changelog generation

Adds the git-workflow skill (Conventional Commits, auto-commit/push
policy, changelog process), CHANGELOG.md seeded from history, and
scripts/generate-changelog.sh to group commits by type. PRs remain
manual by design.

.claude/settings.json

@@ -3,7 +3,16 @@
     "allow": [
       "Bash(winget search *)",
       "Bash(docker compose ps *)",
-      "Bash(docker compose logs *)"
+      "Bash(docker compose logs *)",
+      "Bash(git status*)",
+      "Bash(git diff*)",
+      "Bash(git log*)",
+      "Bash(git add *)",
+      "Bash(git commit *)",
+      "Bash(git push origin main)",
+      "Bash(git push origin *)",
+      "Bash(git tag *)",
+      "Bash(bash scripts/generate-changelog.sh*)"
     ]
   }
 }