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.

CHANGELOG.md

@@ -0,0 +1,13 @@
+# Changelog
+
+All notable changes to this project are documented here.
+
+Format is loosely based on [Keep a Changelog](https://keepachangelog.com/), grouped by
+[Conventional Commits](https://www.conventionalcommits.org/) type. Regenerate the grouped
+entries for a range with `scripts/generate-changelog.sh`; see `.claude/skills/git-workflow/SKILL.md`
+for the full process.
+
+## [Unreleased]
+
+### Chore
+- Initial commit: YouTube Studio Flow (backend, frontend, infrastructure, docs) (d5af006)