feat(db): add feature flags schema for beta feature testing

Add feature_flags and feature_flag_access tables to support controlled
beta testing of new features in production without a separate test environment.

shared/db/migrations/0003_new_senator_kelly.sql

@@ -0,0 +1,25 @@
+CREATE TABLE "feature_flag_access" (
+	"id" serial PRIMARY KEY NOT NULL,
+	"flag_id" integer NOT NULL,
+	"guild_id" bigint,
+	"user_id" bigint,
+	"role_id" bigint,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE TABLE "feature_flags" (
+	"id" serial PRIMARY KEY NOT NULL,
+	"name" varchar(100) NOT NULL,
+	"enabled" boolean DEFAULT false NOT NULL,
+	"description" text,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL,
+	"updated_at" timestamp with time zone DEFAULT now() NOT NULL,
+	CONSTRAINT "feature_flags_name_unique" UNIQUE("name")
+);
+--> statement-breakpoint
+ALTER TABLE "items" ALTER COLUMN "rarity" SET DEFAULT 'C';--> statement-breakpoint
+ALTER TABLE "feature_flag_access" ADD CONSTRAINT "feature_flag_access_flag_id_feature_flags_id_fk" FOREIGN KEY ("flag_id") REFERENCES "public"."feature_flags"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+CREATE INDEX "idx_ffa_flag_id" ON "feature_flag_access" USING btree ("flag_id");--> statement-breakpoint
+CREATE INDEX "idx_ffa_guild_id" ON "feature_flag_access" USING btree ("guild_id");--> statement-breakpoint
+CREATE INDEX "idx_ffa_user_id" ON "feature_flag_access" USING btree ("user_id");--> statement-breakpoint
+CREATE INDEX "idx_ffa_role_id" ON "feature_flag_access" USING btree ("role_id");