ci: sync PR labels from the conventional-commit title (#37784)

Syncs `type/*` and `pr/breaking` labels from the PR title (Conventional
Commits) and folds the existing title lint into the same workflow so
labeling only runs once the title is valid.

- `tools/pr-title.ts`: shared title parser and label mapping.
- `tools/set-pr-labels.ts`: adds/removes labels via the GitHub API.
`type/*` and `pr/breaking` are fully synced (added and removed);
`skip-changelog` (chore/ci) and `topic/build` (build) are only added,
never auto-removed, so manual labeling is preserved.
- `pull-labeler.yml` now hosts `lint-pr-title` and `set-pr-labels`
(`needs: lint-pr-title`) under `pull_request_target`, required so fork
PRs get a writable token. Base-branch checkout only; no PR-head code
runs in the elevated context.
- Removes the superseded `pull-pr-title.yml` and the CI-only
`lint-pr-title` Makefile target.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>

Makefile

@@ -321,10 +321,6 @@ lint-md: node_modules ## lint markdown files
 lint-md-fix: node_modules ## lint markdown files and fix issues
 	pnpm exec markdownlint --fix *.md
 
-.PHONY: lint-pr-title
-lint-pr-title: ## lint PR title against Conventional Commits (set PR_TITLE=...)
-	@node ./tools/lint-pr-title.ts
-
 .PHONY: lint-spell
 lint-spell: ## lint spelling
 	@git ls-files $(SPELLCHECK_FILES) | xargs go run $(MISSPELL_PACKAGE) -dict assets/misspellings.csv -error