feat: per-tier feature toggles for recipe variations/pairings (v0.50.0)

Admins can now disable specific AI features per tier from Admin > Tier
Limits — new feature_flags table (feature x tier -> enabled, defaulting
to true so adding a new gated feature never needs a backfill).

Covers recipe variations, drink pairing, and meal pairing to start.
When disabled for a user's tier, the button stays visible (with a small
lock badge) but opens an upgrade dialog instead of running; the API
route rejects the call server-side either way (requireFeatureEnabled,
re-reads tier from the DB rather than trusting the session's cache,
same rationale as checkAndIncrementTierLimit).

The upgrade dialog is informational only — no Stripe checkout exists
yet (STRIPE_PLAN.md is still just a plan) — its CTA links to /support
prefilled as an upgrade-interest suggestion.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/db/src/schema/feature-flags.ts

@@ -0,0 +1,20 @@
+import { pgTable, text, timestamp, boolean, primaryKey } from "drizzle-orm/pg-core";
+import { relations } from "drizzle-orm";
+import { users, tierEnum } from "./users";
+
+/** Absence of a row for a (featureKey, tier) pair means "enabled" — rows only
+ *  exist to record an override, so adding a new gated feature never requires
+ *  a backfill. */
+export const featureFlags = pgTable("feature_flags", {
+  featureKey: text("feature_key").notNull(),
+  tier: tierEnum("tier").notNull(),
+  enabled: boolean("enabled").notNull().default(true),
+  updatedAt: timestamp("updated_at").notNull().defaultNow(),
+  updatedById: text("updated_by_id").references(() => users.id, { onDelete: "set null" }),
+}, (t) => [
+  primaryKey({ columns: [t.featureKey, t.tier] }),
+]);
+
+export const featureFlagsRelations = relations(featureFlags, ({ one }) => ({
+  updatedBy: one(users, { fields: [featureFlags.updatedById], references: [users.id] }),
+}));

packages/db/src/schema/index.ts

@@ -8,3 +8,4 @@ export * from "./messaging";
 export * from "./billing";
 export * from "./ai-chat";
 export * from "./support";
+export * from "./feature-flags";