fix: use workflow_run trigger in rebuild-site.yml to bypass [skip ci] suppression

[Copilot]

rebuild-site.yml has never fired from the daily pipeline. Bot commits use [skip ci] in the message, which GitHub uses to suppress all push-triggered workflows — including the push: paths: data/processed/** trigger. docs/data/*.json has never been regenerated; the live site has been serving placeholder JSON since launch.

Change

Replace the push trigger with workflow_run, which fires on workflow completion events and is immune to [skip ci]:

# Before
on:
  push:
    branches: [main]
    paths:
      - "data/processed/**"

# After
on:
  workflow_run:
    workflows: ["Pipeline", "Fetch and Process"]
    types: [completed]
    branches: [main]

Add a job-level guard so the rebuild is skipped when the upstream workflow failed:

if: ${{ github.event_name == 'workflow_dispatch' || github.event.workflow_run.conclusion == 'success' }}

The [skip ci] markers on bot commits are intentional and unchanged — this fix only corrects where the site-rebuild trigger listens.