feat: read-only API key scoping

New keys can be created as "Full access" (default, unchanged) or
"Read-only" — read-only keys can only make GET/HEAD/OPTIONS requests,
enforced once in requireSessionOrApiKey (lib/api-auth.ts) rather than in
every route, since a route has no way to know a request came from a
scoped key without that check. Existing keys default to full access —
no behavior change for anyone who doesn't opt in.

Also included in this migration: the chat_messages table for the
next commit (chat history persistence) — generated together since both
touched packages/db/src/schema/users.ts in the same pass.

Verified locally: created both a read-only and a full-access key,
confirmed GET succeeds and POST 403s on the read-only key, confirmed
POST still works on the full-access key, and checked the scope badges
render correctly in the real Settings → API Keys UI.

packages/db/src/schema/ai-chat.ts

@@ -0,0 +1,26 @@
+import { pgTable, text, timestamp, pgEnum, index } from "drizzle-orm/pg-core";
+import { relations } from "drizzle-orm";
+import { users } from "./users";
+import { recipes } from "./recipes";
+
+export const chatRoleEnum = pgEnum("chat_role", ["user", "assistant"]);
+
+// Persists both the per-recipe chat (recipeId set) and the general cooking
+// assistant on the recipes homepage (recipeId null) — same table, since a
+// user searching "their chat history" expects both to show up together.
+export const chatMessages = pgTable("chat_messages", {
+  id: text("id").primaryKey(),
+  userId: text("user_id").notNull().references(() => users.id, { onDelete: "cascade" }),
+  recipeId: text("recipe_id").references(() => recipes.id, { onDelete: "cascade" }),
+  role: chatRoleEnum("role").notNull(),
+  content: text("content").notNull(),
+  createdAt: timestamp("created_at").notNull().defaultNow(),
+}, (t) => [
+  index("chat_messages_user_idx").on(t.userId, t.createdAt),
+  index("chat_messages_recipe_idx").on(t.recipeId),
+]);
+
+export const chatMessagesRelations = relations(chatMessages, ({ one }) => ({
+  user: one(users, { fields: [chatMessages.userId], references: [users.id] }),
+  recipe: one(recipes, { fields: [chatMessages.recipeId], references: [recipes.id] }),
+}));

packages/db/src/schema/index.ts

@@ -6,3 +6,4 @@ export * from "./tiers";
 export * from "./webhooks";
 export * from "./messaging";
 export * from "./billing";
+export * from "./ai-chat";

packages/db/src/schema/users.ts

@@ -12,6 +12,7 @@ import { relations } from "drizzle-orm";
 export const userRoleEnum = pgEnum("user_role", ["user", "moderator", "admin"]);
 export const tierEnum = pgEnum("tier", ["free", "pro"]);
 export const unitPrefEnum = pgEnum("unit_pref", ["metric", "imperial"]);
+export const apiKeyScopeEnum = pgEnum("api_key_scope", ["full", "read"]);
 
 export const users = pgTable("users", {
   id: text("id").primaryKey(),
@@ -96,6 +97,7 @@ export const apiKeys = pgTable("api_keys", {
   userId: text("user_id").notNull().references(() => users.id, { onDelete: "cascade" }),
   name: text("name").notNull(),
   keyHash: text("key_hash").notNull().unique(),
+  scope: apiKeyScopeEnum("scope").notNull().default("full"),
   lastUsedAt: timestamp("last_used_at"),
   createdAt: timestamp("created_at").notNull().defaultNow(),
 });