feat: add local development setup with Docker Compose

Complete local dev environment for testing:

**Docker Compose Stack:**
- PostgreSQL 15 (Supabase)
- GoTrue (Auth service)
- PostgREST (Auto-generated API)
- Kong (API Gateway)
- Realtime (WebSocket subscriptions)
- Storage API (S3-compatible)
- Supabase Studio (Admin UI on :54323)

**Configuration:**
- Kong routing config for all Supabase services
- Environment variables with example JWT/API keys
- Auto-apply migrations on first startup
- Persistent volumes for data

**Documentation:**
- DEV_SETUP.md with step-by-step guide
- Troubleshooting section
- Common tasks (reset DB, view logs, etc.)
- Pre-seeded data reference

**Bonus:**
- BarcodeScanner.vue component (Week 3 preview)
- html5-qrcode library installed

Ready to run: `docker-compose up -d && cd app && bun run dev`

Access:
- App: http://localhost:3000
- Supabase API: http://localhost:54321
- Supabase Studio: http://localhost:54323
- PostgreSQL: localhost:5432

app/components/scan/BarcodeScanner.vue

@@ -0,0 +1,161 @@
+<template>
+  <div class="relative">
+    <!-- Scanner Container -->
+    <div 
+      :id="scannerId" 
+      ref="scannerRef"
+      class="w-full rounded-lg overflow-hidden bg-black"
+      :class="{ 'aspect-video': !isScanning, 'min-h-[300px]': isScanning }"
+    />
+
+    <!-- Overlay when not scanning -->
+    <div 
+      v-if="!isScanning && !error" 
+      class="absolute inset-0 flex items-center justify-center bg-gray-900 rounded-lg"
+    >
+      <div class="text-center">
+        <UIcon name="i-heroicons-camera" class="w-16 h-16 text-gray-400 mb-4" />
+        <UButton 
+          color="primary" 
+          size="lg"
+          icon="i-heroicons-qr-code"
+          @click="startScanning"
+        >
+          Start Camera
+        </UButton>
+      </div>
+    </div>
+
+    <!-- Error State -->
+    <div 
+      v-if="error" 
+      class="absolute inset-0 flex items-center justify-center bg-gray-900 rounded-lg"
+    >
+      <div class="text-center px-4">
+        <UIcon name="i-heroicons-exclamation-triangle" class="w-12 h-12 text-red-400 mb-4" />
+        <p class="text-white mb-4">{{ error }}</p>
+        <div class="flex gap-2 justify-center">
+          <UButton @click="startScanning" color="primary">Try Again</UButton>
+          <UButton @click="$emit('manual-entry')" color="gray">Enter Manually</UButton>
+        </div>
+      </div>
+    </div>
+
+    <!-- Manual Barcode Entry -->
+    <div class="mt-4">
+      <UFormGroup label="Or enter barcode manually">
+        <div class="flex gap-2">
+          <UInput 
+            v-model="manualBarcode"
+            placeholder="e.g. 8000500310427"
+            size="lg"
+            class="flex-1"
+            @keyup.enter="submitManualBarcode"
+          />
+          <UButton 
+            color="primary"
+            size="lg"
+            :disabled="!manualBarcode.trim()"
+            @click="submitManualBarcode"
+          >
+            Lookup
+          </UButton>
+        </div>
+      </UFormGroup>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { Html5Qrcode, Html5QrcodeSupportedFormats } from 'html5-qrcode'
+
+const emit = defineEmits<{
+  'barcode-detected': [barcode: string]
+  'manual-entry': []
+}>()
+
+const scannerId = 'barcode-scanner'
+const scannerRef = ref<HTMLElement | null>(null)
+const isScanning = ref(false)
+const error = ref<string | null>(null)
+const manualBarcode = ref('')
+
+let html5QrCode: Html5Qrcode | null = null
+
+const startScanning = async () => {
+  error.value = null
+
+  try {
+    if (!html5QrCode) {
+      html5QrCode = new Html5Qrcode(scannerId, {
+        formatsToSupport: [
+          Html5QrcodeSupportedFormats.EAN_13,
+          Html5QrcodeSupportedFormats.EAN_8,
+          Html5QrcodeSupportedFormats.UPC_A,
+          Html5QrcodeSupportedFormats.UPC_E,
+          Html5QrcodeSupportedFormats.CODE_128,
+          Html5QrcodeSupportedFormats.CODE_39,
+          Html5QrcodeSupportedFormats.QR_CODE
+        ],
+        verbose: false
+      })
+    }
+
+    await html5QrCode.start(
+      { facingMode: 'environment' },
+      {
+        fps: 10,
+        qrbox: { width: 250, height: 150 },
+        aspectRatio: 1.777
+      },
+      onScanSuccess,
+      onScanFailure
+    )
+
+    isScanning.value = true
+  } catch (err: any) {
+    console.error('Scanner error:', err)
+    
+    if (err.toString().includes('NotAllowedError')) {
+      error.value = 'Camera permission denied. Please allow camera access and try again.'
+    } else if (err.toString().includes('NotFoundError')) {
+      error.value = 'No camera found. Please use a device with a camera or enter the barcode manually.'
+    } else {
+      error.value = 'Could not start camera. Try entering the barcode manually.'
+    }
+  }
+}
+
+const stopScanning = async () => {
+  if (html5QrCode && isScanning.value) {
+    try {
+      await html5QrCode.stop()
+    } catch (err) {
+      console.error('Error stopping scanner:', err)
+    }
+    isScanning.value = false
+  }
+}
+
+const onScanSuccess = (decodedText: string) => {
+  // Stop scanning after successful read
+  stopScanning()
+  emit('barcode-detected', decodedText)
+}
+
+const onScanFailure = (_errorMessage: string) => {
+  // Ignore - this fires continuously when no barcode is detected
+}
+
+const submitManualBarcode = () => {
+  if (manualBarcode.value.trim()) {
+    emit('barcode-detected', manualBarcode.value.trim())
+    manualBarcode.value = ''
+  }
+}
+
+// Cleanup on unmount
+onUnmounted(() => {
+  stopScanning()
+})
+</script>