Update provisioning to auto-detect forecast zones from AFP

[rchlfryn]

Description

Auto-detect single vs multi-zone avalanche centers from AFP data during provisioning, and create the appropriate zone-specific built-in pages. Non-forecast built-in pages are now sourced from DVAC's navigation rather than a hardcoded list, so changes to the template automatically propagate to new tenants. Mountain Weather is conditionally provisioned based on whether the center has weather forecasts configured in NAC.

Related Issues

Fixes #999

Key Changes

• Zone-aware provisioning — provisionTenant.ts calls getActiveForecastZones() during provisioning. Single-zone centers get one "Avalanche Forecast" page; multi-zone centers get "All Forecasts" + per-zone pages sorted by rank. Falls back to a default "All Forecasts" page if AFP is unavailable.
• DVAC as source of truth for non-forecast built-in pages — Instead of a hardcoded BUILT_IN_PAGES list, non-forecast pages (weather stations, observations, blog, events, etc.) are extracted directly from DVAC's resolved navigation (depth: 1). extractNavReferences now returns { title, url } pairs so no separate DB query is needed.
• Mountain Weather from NAC — Mountain Weather (/weather/forecast) is no longer sourced from DVAC's nav. It's conditionally included based on whether the center has platforms.weather enabled in NAC.
• Zone-aware navigation — Provisioning now populates the forecasts tab (single zone: direct link; multi-zone: "All Forecasts" + per-zone items) and the observations tab with built-in page links. Also adds missing blog and events tab data that was causing nav creation to silently fail.
• Split checklist items — "Built-in pages" in the onboarding checklist is now two items: "Forecast Built-In pages" and "Default Built-In pages", each with their own count.
• Shared resolveBuiltInPages function — Deduplicates the AFP query + page resolution logic between provisionTenant.ts and onboardingActions.ts.

How to test

1. Run pnpm seed to seed the database
2. Go to /admin/collections/tenants and create a new tenant (e.g. name: "Test Center", slug: "btac")
3. Verify the onboarding checklist shows separate "Forecast Built-In pages" and "Default Built-In pages" counts
   • For a multi-zone center like btac (4 zones), verify "All Forecasts" + 4 zone pages are created as built-in pages
   • For a single-zone center like msac), verify a single "Avalanche Forecast" built-in page is created
4. Verify Mountain Weather is only created for centers with weather forecasts in NAC
5. Verify navigation is created with forecast zone links populated
6. Run pnpm test — all 289 tests pass

Screenshots / Demo video

https://www.loom.com/share/0563513b68564b3d8265cdba9ec9519b

Migration Explanation

No new migrations in this PR's scope (provisioning changes only).

Future enhancements / Questions

• The onboarding status check calls AFP on every checklist load — could cache the zone count if this becomes a performance concern (likely not)

[github-actions]

Preview deployment: https://provisioning-updates.preview.avy-fx.org