feat: add Request and Job schema with migration

Adds the Prisma schema (Request/Job models, RequestStatus/JobState
enums), a Prisma client singleton at web/src/lib/db.ts, and the
init_request_job migration, applied and verified against Postgres.

Also publishes the db service's port (5432:5432) in docker-compose.yml
so host-run Prisma commands can reach localhost:5432 for local dev.

web/prisma/migrations/20260710144250_init_request_job/migration.sql

@@ -0,0 +1,37 @@
+-- CreateEnum
+CREATE TYPE "RequestStatus" AS ENUM ('pending', 'completed', 'needs_attention');
+
+-- CreateEnum
+CREATE TYPE "JobState" AS ENUM ('requested', 'matching', 'matched', 'downloading', 'tagging', 'imported', 'needs_attention');
+
+-- CreateTable
+CREATE TABLE "Request" (
+    "id" TEXT NOT NULL,
+    "artist" TEXT NOT NULL,
+    "album" TEXT NOT NULL,
+    "status" "RequestStatus" NOT NULL DEFAULT 'pending',
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "Request_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "Job" (
+    "id" TEXT NOT NULL,
+    "requestId" TEXT NOT NULL,
+    "state" "JobState" NOT NULL DEFAULT 'requested',
+    "currentStage" TEXT NOT NULL DEFAULT 'intake',
+    "attempts" INTEGER NOT NULL DEFAULT 0,
+    "error" TEXT,
+    "claimedAt" TIMESTAMP(3),
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "Job_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "Job_requestId_key" ON "Job"("requestId");
+
+-- AddForeignKey
+ALTER TABLE "Job" ADD CONSTRAINT "Job_requestId_fkey" FOREIGN KEY ("requestId") REFERENCES "Request"("id") ON DELETE CASCADE ON UPDATE CASCADE;

web/prisma/migrations/migration_lock.toml

@@ -0,0 +1,3 @@
+# Please do not edit this file manually
+# It should be added in your version-control system (e.g., Git)
+provider = "postgresql"