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/src/capture/Resume.svelte

@@ -0,0 +1,28 @@
+<script lang="ts">
+  export let onContinue: () => void;
+  export let onFresh: () => void;
+</script>
+
+<section class="panel">
+  <h1>Resume?</h1>
+  <p>You have an in-progress slab on this device.</p>
+  <div class="row">
+    <button class="primary" type="button" on:click={onContinue}>Continue</button>
+    <button class="ghost" type="button" on:click={onFresh}>Start fresh</button>
+  </div>
+</section>
+
+<style>
+  .panel { padding: 24px 16px; text-align: center; color: #eee; }
+  h1 { font-size: 1.4rem; }
+  p { color: #aaa; }
+  .row { display: flex; gap: 12px; justify-content: center; margin-top: 24px; }
+  .primary {
+    flex: 1; max-width: 200px; padding: 14px; font-size: 1.05rem; border-radius: 10px; border: 0;
+    background: #00e5ff; color: #002; font-weight: 700;
+  }
+  .ghost {
+    flex: 1; max-width: 200px; padding: 14px; border-radius: 10px; border: 1px solid #444;
+    background: transparent; color: #ccc;
+  }
+</style>