feat(subscriptions): database-backed plan designer with admin CRUD and overage buffer

- Add SubscriptionPlan model and subscription_plans table (migration 015)
- Add billing cycle/period/allow_overage fields to UserProfile (migration 016)
- Add subscription_overage_percent config field (replaces overage_factor)
- Rewrite check_upload_allowed: use overage_percent, yearly carry-over, no daily cap
- Add seed_default_plans(), _plan_to_dict(), get_year_file_count(), _months_elapsed()
- Update get_tier/get_all_tiers to be DB-first with TIER_DEFAULTS fallback
- Add TIER_DEFAULTS alias (TIERS kept for backward compat)
- New /api/plans/ CRUD endpoints (admin-only except list/get)
- New /admin/plans Plan Designer page with Alpine.js UI
- Add Plan Designer link to admin navigation in base.html
- Remove 'Files per day' row from pricing comparison table
- Add billing cycle + period start to admin users edit modal
- Seed default plans on startup in lifespan handler
- Rewrite docs/SubscriptionTiers.md with full plan/overage/API docs
- Fix all tests in test_subscription.py (remove daily cap tests, add overage/carry-over tests)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

app/views/__init__.py

@@ -14,11 +14,12 @@ from app.views.general import router as general_router
 from app.views.google_drive import router as google_drive_router
 from app.views.license_routes import router as license_router  # Add the license router
 from app.views.onedrive import router as onedrive_router
+from app.views.plans import router as plans_router  # Admin Plan Designer
 from app.views.queue import router as queue_router
 from app.views.search import router as search_router
 from app.views.settings import router as settings_router
 from app.views.status import router as status_router
-from app.views.subscriptions import router as subscriptions_router
+from app.views.subscriptions import router as subscriptions_router  # Pricing + subscription pages
 from app.views.wizard import router as wizard_router
 
 # Create a main router that includes all the view routers
@@ -37,3 +38,4 @@ router.include_router(filemanager_router)
 router.include_router(search_router)
 router.include_router(queue_router)
 router.include_router(subscriptions_router)  # Pricing + subscription pages
+router.include_router(plans_router)  # Admin Plan Designer