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

packages/db/src/schema/users.ts

@@ -10,7 +10,7 @@ import {
 import { relations } from "drizzle-orm";
 
 export const userRoleEnum = pgEnum("user_role", ["user", "moderator", "admin"]);
-export const tierEnum = pgEnum("tier", ["free", "pro", "team"]);
+export const tierEnum = pgEnum("tier", ["free", "pro", "family"]);
 export const unitPrefEnum = pgEnum("unit_pref", ["metric", "imperial"]);
 export const apiKeyScopeEnum = pgEnum("api_key_scope", ["full", "read"]);