Align Pages Job Triggers with Website Change Detection

The current Pages stage runs on every push to main, even when no website files were modified. This leads to avoidable pipeline failures, as the stage waits on the docs-to-pdf job, which only executes when CI configuration or website content changes. We should tighten the trigger conditions and document the full trigger matrix so this pattern is clear and not overlooked again.

Acceptance Criteria:

• Update the rules: for the Pages job so it triggers only when files under the website/ directory change.
• Document the trigger matrix for related jobs to prevent future inconsistencies.
• Confirm compatibility across existing dependent and upstream jobs.
• Verify expected pipeline behaviour with both matching and non-matching changes.