ci: add PR title linting (Conventional Commits)

[hasansezertasan]

Context

Adopt PR-title linting (from #16) so PR titles follow Conventional Commits — matching the repo's PR-title convention and enabling downstream label/changelog automation.

Source workflow uses amannn/action-semantic-pull-request on pull_request_target with permissions: pull-requests: read.

Proposed tasks

• Add .github/workflows/pr-title.yml running amannn/action-semantic-pull-request
• SHA-pin the action + top-level permissions: {} + minimal pull-requests: read (to pass the zizmor gate from ci: adopt zizmor for GitHub Actions security #22/ci: adopt zizmor and harden GitHub Actions workflows #39)
• Confirm the allowed types match our Conventional Commits usage

Notes

• Safe use of pull_request_target: this workflow only reads the PR title; it must not check out or run PR head code.