feat: add release notes draft command

[marcus]

Summary

• add a new \ command that drafts markdown release notes from git history since the latest tag or an explicit revision range
• add reusable git helpers plus a small release-notes domain package for classification and rendering
• document the maintainer workflow and cover the feature with git/release/cmd tests

Testing

• go test ./internal/git ./internal/release ./cmd
• env -u TD_FEATURE_SYNC_AUTOSYNC -u TD_FEATURE_SYNC_CLI go test ./...
• go run . release-notes --output markdown --include-files --include-stats