feat(capture): ship Milestone 1 browser capture app

Why
Phone and PC need a single capture flow that ends at inventory PNG and
board-foot numbers with no backend, inference, or Woo create.

Scope
Add frontend/ Vite+Svelte capture UI with Resume, Add photo, Mask,
Length axis, and Measure. Mask runs in a worker with Auto/Green/Black
and a 2.0s sensitivity debounce. Measure computes scale, widths, sqft,
bdft, and a 3:4 alpha inventory PNG. Persist one device draft in
IndexedDB. Serve the static build from frontend/Dockerfile via nginx
(deploy/nginx-m1.conf). No FastAPI.

Verification
sudo docker build -f frontend/Dockerfile -t slabuploader-m1 .
sudo docker run -d --name slabuploader-m1 -p 0.0.0.0:18080:80 slabuploader-m1
curl http://127.0.0.1:18080/ returns 200
Playwright: synthetic green-sheet photo through Calculate shows sqft/bdft

frontend/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "slabuploader-frontend",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc --noEmit && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "idb-keyval": "^6.3.0",
+    "svelte": "^4.2.20"
+  },
+  "devDependencies": {
+    "@sveltejs/vite-plugin-svelte": "^3.1.2",
+    "svelte-preprocess": "^5.1.4",
+    "typescript": "^5.7.3",
+    "vite": "^5.4.19"
+  }
+}