Raise alerts: failed or paused prints, and AI detections

Nothing subscribed to channel:print_alerts and nothing watched a printer
fail, so an operator away from the screen found out when they came back to
a ruined plate. Alerts are now rows in printer_alerts, listed at
GET /alerts (open=true for what still needs a person) and cleared with
POST /alerts/:id/acknowledge, which is operator-only and keeps the first
acknowledger on the record.

Two sources. Telemetry: a change into error is a failed print if the printer
was printing or paused, otherwise a printer error; a print the printer
paused itself (how an AMS fault looks) is announced too. Transitions, not
levels - a printer sitting in error is one alert, not one per frame - and a
connection's first sight of a printer raises nothing, so a gateway that
reconnects does not re-announce known faults. AI: the worker's Valkey
publications are stored when confidence is at least ALERT_MIN_CONFIDENCE
(default 0.6); the worker deliberately does not threshold, so the policy
lives here. A bad message costs one message, not the listener.

e2e-authz.sh gains the scoping/ack cases; new e2e-alerts.sh drives a stand-in
gateway over the real /ws/edge/v1 and the real Valkey channel (checked to
fail when the derivation is broken).

drizzle/0004_printer_alerts.sql

@@ -0,0 +1,32 @@
+DO $$ BEGIN
+ CREATE TYPE "public"."alert_kind" AS ENUM('print_failed', 'print_paused', 'printer_error', 'ai_detection');
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+CREATE TABLE IF NOT EXISTS "printer_alerts" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"farm_id" uuid NOT NULL,
+	"printer_id" uuid,
+	"kind" "alert_kind" NOT NULL,
+	"message" text NOT NULL,
+	"confidence" real,
+	"object_key" text,
+	"acknowledged_by" uuid,
+	"acknowledged_at" timestamp with time zone,
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "printer_alerts" ADD CONSTRAINT "printer_alerts_farm_id_farms_id_fk" FOREIGN KEY ("farm_id") REFERENCES "public"."farms"("id") ON DELETE cascade ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "printer_alerts" ADD CONSTRAINT "printer_alerts_printer_id_printers_id_fk" FOREIGN KEY ("printer_id") REFERENCES "public"."printers"("id") ON DELETE set null ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "printer_alerts_farm_open_idx" ON "printer_alerts" USING btree ("farm_id","acknowledged_at");