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/migrations/0035_gifted_plazm.sql

@@ -0,0 +1,16 @@
+CREATE TYPE "public"."api_key_scope" AS ENUM('full', 'read');--> statement-breakpoint
+CREATE TYPE "public"."chat_role" AS ENUM('user', 'assistant');--> statement-breakpoint
+CREATE TABLE "chat_messages" (
+	"id" text PRIMARY KEY NOT NULL,
+	"user_id" text NOT NULL,
+	"recipe_id" text,
+	"role" "chat_role" NOT NULL,
+	"content" text NOT NULL,
+	"created_at" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "api_keys" ADD COLUMN "scope" "api_key_scope" DEFAULT 'full' NOT NULL;--> statement-breakpoint
+ALTER TABLE "chat_messages" ADD CONSTRAINT "chat_messages_user_id_users_id_fk" FOREIGN KEY ("user_id") REFERENCES "public"."users"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "chat_messages" ADD CONSTRAINT "chat_messages_recipe_id_recipes_id_fk" FOREIGN KEY ("recipe_id") REFERENCES "public"."recipes"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+CREATE INDEX "chat_messages_user_idx" ON "chat_messages" USING btree ("user_id","created_at");--> statement-breakpoint
+CREATE INDEX "chat_messages_recipe_idx" ON "chat_messages" USING btree ("recipe_id");

packages/db/src/migrations/meta/_journal.json

@@ -246,6 +246,13 @@
       "when": 1783875228288,
       "tag": "0034_dapper_nocturne",
       "breakpoints": true
+    },
+    {
+      "idx": 35,
+      "version": "7",
+      "when": 1783887815564,
+      "tag": "0035_gifted_plazm",
+      "breakpoints": true
     }
   ]
 }