feat(matching): add auto-matching system for recording partners

Implement algorithm to match dancers with recorders based on:
- Heat collision avoidance (division + competitionType + heatNumber)
- Buffer time (1 heat after dancing before can record)
- Location preference (same city > same country > anyone)
- Max 3 recordings per person
- Opt-out support (falls to bottom of queue)

New API endpoints:
- PUT /events/:slug/registration-deadline
- PUT /events/:slug/recorder-opt-out
- POST /events/:slug/run-matching
- GET /events/:slug/match-suggestions
- PUT /events/:slug/match-suggestions/:id/status

Database changes:
- Event: registrationDeadline, matchingRunAt
- EventParticipant: recorderOptOut
- RecordingSuggestion: new model for match suggestions

backend/prisma/migrations/20251123172500_add_auto_matching/migration.sql

@@ -0,0 +1,37 @@
+-- AlterTable
+ALTER TABLE "event_participants" ADD COLUMN     "recorder_opt_out" BOOLEAN NOT NULL DEFAULT false;
+
+-- AlterTable
+ALTER TABLE "events" ADD COLUMN     "matching_run_at" TIMESTAMP(3),
+ADD COLUMN     "registration_deadline" TIMESTAMP(3);
+
+-- CreateTable
+CREATE TABLE "recording_suggestions" (
+    "id" SERIAL NOT NULL,
+    "event_id" INTEGER NOT NULL,
+    "heat_id" INTEGER NOT NULL,
+    "recorder_id" INTEGER,
+    "status" VARCHAR(20) NOT NULL DEFAULT 'pending',
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updated_at" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "recording_suggestions_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "recording_suggestions_heat_id_key" ON "recording_suggestions"("heat_id");
+
+-- CreateIndex
+CREATE INDEX "recording_suggestions_event_id_idx" ON "recording_suggestions"("event_id");
+
+-- CreateIndex
+CREATE INDEX "recording_suggestions_recorder_id_idx" ON "recording_suggestions"("recorder_id");
+
+-- AddForeignKey
+ALTER TABLE "recording_suggestions" ADD CONSTRAINT "recording_suggestions_event_id_fkey" FOREIGN KEY ("event_id") REFERENCES "events"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "recording_suggestions" ADD CONSTRAINT "recording_suggestions_heat_id_fkey" FOREIGN KEY ("heat_id") REFERENCES "event_user_heats"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "recording_suggestions" ADD CONSTRAINT "recording_suggestions_recorder_id_fkey" FOREIGN KEY ("recorder_id") REFERENCES "users"("id") ON DELETE SET NULL ON UPDATE CASCADE;