Phase 1: Per-project cache tag invalidation on dashboard

[dkwiebe]

Summary

The dashboard API caches responses for 5 minutes using a flat key. This means users always see stale data and there's no way to bust the cache when new webhook events arrive for a specific project.

Implementation

In app/Http/Controllers/DashboardController.php, switch to tagged cache:

Cache::tags(['project-' . implode('-', $sortedProjectIds)])->remember($key, 300, fn() => ...);

After writing events in the webhook Job (see Phase 2 queuing issue), flush the relevant tag:

Cache::tags(['project-' . $project->id])->flush();

Note: Requires a cache driver that supports tags (Redis or Memcached). Add a conditional fallback for file/database drivers that skips tagging.

Acceptance Criteria

• Dashboard reflects new events within seconds of arrival (when using Redis/Memcached)
• Falls back gracefully to the existing 5-minute TTL if tags aren't supported
• Cache is flushed per project, not globally