build(ci): Prune unpromoted Velox premerge workflows

[sperlingxx]

Summary

• Remove automatic pull-request triggers from eight broad Velox build, fuzzer, packaging, and compatibility workflows that have not satisfied Issue CI roadmap: restore Velox and Spark-MPP premerge coverage incrementally #27's promotion policy.
• Suspend the five review/comment/workflow-run helpers that only make sense while the inherited Linux and fuzzer PR lanes are active.
• Preserve the existing preliminary, Breeze, documentation, and labeler PR surface, together with manual, scheduled, and upstream-push entry points where applicable.

Boundary

This is the trigger-only premerge pruning slice from Issue #27, reapplied from current dev rather than rebasing stale draft PR #25.

It does not:

• change Velox source, build scripts, test selection, or reusable native workflow implementation;
• change Blossom, Jenkins, the dependency graph workflow, or repository protection settings;
• add the Phase 0 classifier/aggregate from PR build(ci): Add lightweight Velox premerge gate #25;
• enable or claim Phase 2/3 native or Spark-MPP coverage.

The existing broad PR triggers currently create queued or skipped checks in this fork without proving native execution. Issue #27 requires these lanes to remain manual, scheduled, or path-selected canaries until their runners, commands, aggregate status, runtime, and ownership satisfy the promotion policy.

Validation

• uvx pre-commit run --files <13 changed workflows>
  • YAML lint/format: passed
  • zizmor: passed
  • GitHub Actions workflow validation: passed
  • repository license and workflow-image checks: passed
• git diff --check: passed
• Final trigger inventory leaves direct pull_request workflows only in breeze.yml, docs.yml, and preliminary_checks.yml; labeler.yml retains its existing pull_request_target metadata path.
• Independent scope review found no source, Blossom, dependency-graph, Breeze, docs, preliminary-check, or labeler changes.

Related: #27