Sync planning items to Google Calendar

When you have Gmail + Calendar connected (Settings → Integrations), planning items can flow into your primary Google Calendar.

Per-item:
• Each row in the Tasks tab has a small **+ cal** pill on the right. Click to add that task or milestone as an all-day event on your Calendar; click again to remove it. The pill turns green ("✓ on cal") when synced.

Bulk sync milestones:
• On the Tasks tab, click **Sync milestones to Google Calendar** to push every milestone in one batch.

What gets synced:
• Title = task / milestone / phase name
• Date(s) = start → end (single-day for milestones)
• Description = the task's description plus a note that it came from Turtini Planning, including the project name

Duplicate-safe:
• Re-syncing the same item updates the existing event in place, never duplicates. The sync ledger lives at `users/{uid}/planningCalendarSync`.
• Deleting the event in Calendar is fine — next sync recreates it cleanly.

Privacy:
• Sync is **per-user**. Your teammates' calendars are untouched. Each project member can sync (or not) independently.

Wally can sync too: "Add the foundation pour to my Google Calendar" or "Sync all milestones for the renovation project to my calendar" — confirm-first action card.