fix: make gates transparent about fork PR skip behavior

- Remove `if: always()` from integration-gate, coverage-gate, codecov-gate, pipeline-gate
- Gates now naturally skip when their upstream dependencies are skipped (fork PR behavior)
- Prevents confusing "complete" status when nothing actually ran
- Fork PRs will show "skipped" in UI instead of obscuring behavior behind gate success
- Aligns with GitHub Actions standard job dependency semantics

.github/workflows/supply-chain-pr.yml

@@ -9,11 +9,6 @@ on:
         description: "PR number to verify (optional, will auto-detect from workflow_run)"
         required: false
         type: string
-  workflow_run:
-    workflows:
-      - Docker Build, Publish & Test
-    types:
-      - completed
 
 concurrency:
   group: supply-chain-pr-${{ github.event.workflow_run.event || github.event_name }}-${{ github.event.workflow_run.head_branch || github.ref }}