Two concurrent series lanes, Complete studies, self-paced finished books; v2.9.0

- Study status 'complete' (manual or auto when all lessons released); stays enrollable and self-paced (no sequential lock, Resume button, Finished Studies hub section)
- Studies get lane (A/B) and expected start date; planned studies show "Starts <date>"; hub shows next lesson date instead of hardcoded pace
- Second concurrent series (homepage card, admin panel) with its own scheduled launch; transitions are per lane and flip the ending study to Complete and the incoming study to Active
- Finished books link to their study: "Study This Book" on playlist page, audio-only link from hub (playlist stays public, no account)
- Admin: bulk release scheduler (every N days), same-day collision warning, linked-study selects
- Weekly digest no longer dumps a finished study's backlog on late enrollees
- CI: build and tag the container as :beta on pushes to the beta branch

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.8.5",
+  "version": "2.9.0",
   "type": "module",
   "scripts": {
     "dev": "vite",