feat: add STEM file support per track

- DB: stems table with trackId FK, fileKey, sortOrder, createdById
- API: GET/POST/DELETE stems, presigned upload URL, ZIP download via fflate
- Web: StemUploadDropzone (multi-file, batch upload, progress bars)
- Web: StemList with download-all-ZIP and per-stem delete
- Web: STEMs tab in track detail view
- Icon: add 'music' icon to inline set
- Auto-migration runs stems table creation on boot

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/src/migrations/0006_brown_lily_hollister.sql

@@ -0,0 +1,15 @@
+CREATE TABLE "stems" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"track_id" uuid NOT NULL,
+	"name" varchar(255) NOT NULL,
+	"original_file_name" varchar(500) NOT NULL,
+	"mime_type" varchar(100) NOT NULL,
+	"file_size" bigint NOT NULL,
+	"file_key" text NOT NULL,
+	"sort_order" integer DEFAULT 0 NOT NULL,
+	"created_by_id" uuid NOT NULL,
+	"created_at" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "stems" ADD CONSTRAINT "stems_track_id_tracks_id_fk" FOREIGN KEY ("track_id") REFERENCES "public"."tracks"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "stems" ADD CONSTRAINT "stems_created_by_id_users_id_fk" FOREIGN KEY ("created_by_id") REFERENCES "public"."users"("id") ON DELETE no action ON UPDATE no action;

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

@@ -43,6 +43,13 @@
       "when": 1776012912970,
       "tag": "0005_rare_triathlon",
       "breakpoints": true
+    },
+    {
+      "idx": 6,
+      "version": "7",
+      "when": 1776094119472,
+      "tag": "0006_brown_lily_hollister",
+      "breakpoints": true
     }
   ]
 }

packages/db/src/schema/tracks.ts

@@ -77,3 +77,20 @@ export const versions = pgTable('versions', {
     .notNull(),
   createdAt: timestamp('created_at').defaultNow().notNull(),
 });
+
+export const stems = pgTable('stems', {
+  id: uuid('id').defaultRandom().primaryKey(),
+  trackId: uuid('track_id')
+    .references(() => tracks.id, { onDelete: 'cascade' })
+    .notNull(),
+  name: varchar('name', { length: 255 }).notNull(),
+  originalFileName: varchar('original_file_name', { length: 500 }).notNull(),
+  mimeType: varchar('mime_type', { length: 100 }).notNull(),
+  fileSize: bigint('file_size', { mode: 'number' }).notNull(),
+  fileKey: text('file_key').notNull(),
+  sortOrder: integer('sort_order').default(0).notNull(),
+  createdById: uuid('created_by_id')
+    .references(() => users.id)
+    .notNull(),
+  createdAt: timestamp('created_at').defaultNow().notNull(),
+});