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/ai/ai-error.ts

@@ -54,7 +54,7 @@ type QuotaResult<T> = { ok: true; data: T } | { ok: false; response: NextRespons
  */
 export async function withAiQuota<T>(
   userId: string,
-  tier: "free" | "pro" | "team",
+  tier: "free" | "pro" | "family",
   fn: () => Promise<T>,
   opts?: { skipQuota?: boolean }
 ): Promise<QuotaResult<T>> {