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/lib/invites.ts

@@ -27,7 +27,7 @@ export async function createInvite(opts: {
   createdById: string;
   email?: string | null;
   role?: "user" | "moderator" | "admin";
-  tier?: "free" | "pro" | "team";
+  tier?: "free" | "pro" | "family";
   expiresInDays?: number | null;
 }) {
   const [invite] = await db