ci: move PR report inline to ci.yml, delete ci-report.yml

The old ci-report.yml used workflow_run which always runs code from
the default branch (main). This meant the PR comment used main's
stale report template that still referenced the old unit/integration
split architecture — causing "Merge coverage reports" failures.

Moving the report inline to ci.yml means it runs from the PR branch
and uses the current report template. The report now shows:
- per-platform status (Ubuntu/Windows/macOS columns)
- unified test counts from the single vitest run
- coverage with base branch (main) delta comparison
- commit SHA for traceability

Also removes the save-pr-meta job since the report no longer needs
a separate workflow_run trigger.

Author: magyargergo