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/components/admin/create-user-dialog.tsx

@@ -16,7 +16,7 @@ export function CreateUserDialog() {
   const [email, setEmail] = useState("");
   const [name, setName] = useState("");
   const [role, setRole] = useState<"user" | "moderator" | "admin">("user");
-  const [tier, setTier] = useState<"free" | "pro" | "team">("free");
+  const [tier, setTier] = useState<"free" | "pro" | "family">("free");
   const [saving, setSaving] = useState(false);
 
   async function handleCreate() {
@@ -85,7 +85,7 @@ export function CreateUserDialog() {
                   <SelectContent>
                     <SelectItem value="free">Free</SelectItem>
                     <SelectItem value="pro">Pro</SelectItem>
-                    <SelectItem value="team">Team</SelectItem>
+                    <SelectItem value="family">Family</SelectItem>
                   </SelectContent>
                 </Select>
               </div>