rename: "Team" billing tier to "Family"

All literal "team" tier-value references renamed to "family" across
API routes, admin UI, OpenAPI schemas, and lib/tiers.ts. The DB enum
value itself is renamed in place via ALTER TYPE ... RENAME VALUE
(migration 0044) rather than drizzle-kit's auto-generated
drop-and-recreate-the-enum migration, which would have failed against
any existing row still holding 'team' — RENAME VALUE preserves
existing data with no cast/backfill needed.

Also adds STRIPE_PLAN.md — a full Stripe billing integration plan
(Checkout+Portal, tier→Price mapping, admin billing dashboard, and a
multi-user Family-group design since Family is meant to cover several
accounts under one subscription, not one payer). Planning only, no
Stripe code yet.

v0.47.0

apps/web/app/api/v1/admin/tiers/[tier]/route.ts

@@ -16,7 +16,7 @@ export async function PATCH(req: NextRequest, { params }: RouteContext) {
   if (response) return response;
 
   const { tier } = await params;
-  if (tier !== "free" && tier !== "pro" && tier !== "team") {
+  if (tier !== "free" && tier !== "pro" && tier !== "family") {
     return NextResponse.json({ error: "Invalid tier" }, { status: 400 });
   }