chore(ci): revert consolidated pipeline and restore individual workflow triggers

Reverts the experimental consolidated CI pipeline strategy in favor of independent, parallel workflows triggered on pull requests.

- Removed .github/workflows/ci-pipeline.yml
- Restored 'on: pull_request' triggers to:
  - docker-build.yml
  - cerberus-integration.yml
  - crowdsec-integration.yml
  - rate-limit-integration.yml
  - waf-integration.yml
  - e2e-tests-split.yml
- Updated integration workflows to build local Docker images instead of expecting artifacts
- Fixed invalid 'env' context usage in e2e-tests-split.yml conditions

.github/workflows/security-pr.yml

@@ -10,6 +10,7 @@ on:
         description: 'PR number to scan (optional)'
         required: false
         type: string
+  pull_request:
 
 concurrency:
   group: security-pr-${{ github.event.workflow_run.event || github.event_name }}-${{ github.event.workflow_run.head_branch || github.ref }}
@@ -23,6 +24,7 @@ jobs:
     # Run for: manual dispatch, PR builds, or any push builds from docker-build
     if: >-
       github.event_name == 'workflow_dispatch' ||
+      github.event_name == 'pull_request' ||
       ((github.event.workflow_run.event == 'push' || github.event.workflow_run.pull_requests[0].number != null) &&
        (github.event.workflow_run.status != 'completed' || github.event.workflow_run.conclusion == 'success'))