Add label_dispatch trigger and generated cross-repo .remote.yml bridge workflows

[Copilot]

This change adds a first-class on.label_dispatch trigger for CentralRepoOps-style label routing across repositories. Instead of trying to make cross-repo label events native in a single workflow, the compiler now emits a bridge pattern directly: a central repository_dispatch listener plus a generated remote label-trigger workflow.

• Trigger model

  • Added on.label_dispatch support in frontmatter extraction and workflow data.
  • Supports:
    • shorthand: label_dispatch: ns-pattern-review
    • object: label_dispatch: { label, allowed-repos }
  • Added schema coverage in main_workflow_schema.json.

• Central workflow compilation

  • When label_dispatch is present, compiled on: now includes:
    • repository_dispatch with workflow-specific event type (gh_aw_label_dispatch__<workflow-id>)
    • workflow_dispatch fallback
  • Injects a dispatch guard condition checking:
    • client_payload.trigger_label
    • optional repo allowlist matching from allowed-repos (owner/repo, owner/*, *).

• Generated remote bridge workflow

  • Added post-processing generator for <workflow-id>.remote.yml.
  • Generated bridge workflow:
    • listens on pull_request labeled
    • validates trigger label and optional allowed repos
    • dispatches to the central repo via repos.createDispatchEvent with typed payload fields:
      target_repo, pr_number, head_sha, base_sha, trigger_label, delivery_id, actor
  • Removes stale .remote.yml when label_dispatch is removed.

• Docs

  • Added Label Dispatch Trigger (label_dispatch) section to trigger reference with CentralRepoOps bridge semantics.

on:
  label_dispatch:
    label: ns-pattern-review
    allowed-repos:
      - my-org/*