feat(proxy): add image tracing endpoint

Add GET /trace which fetches an image, traces it into a vector shape, and returns the result BSON-encoded. Tracing is configurable via mode (alpha, bw, color) and format (shape, svg). The shape format parses the vtracer SVG into an outline/holes polygon matching @tts/mesh's Shape interface.

packages/shared/src/schemas.test.ts

@@ -5,6 +5,7 @@ import {
   itemIdSchema,
   searchQuerySchema,
   searchResultSchema,
+  traceRequestSchema,
   workshopItemSchema,
 } from './schemas.js';
 
@@ -132,4 +133,56 @@ describe('searchResultSchema', () => {
     const result = { items: [], page: 1, hasMore: false };
     expect(searchResultSchema.parse(result)).toEqual(result);
   });
+});
+
+describe('traceRequestSchema', () => {
+  it('defaults mode, threshold, and format', () => {
+    expect(traceRequestSchema.parse({ url: 'https://example.com/a.png' })).toEqual({
+      url: 'https://example.com/a.png',
+      mode: 'alpha',
+      threshold: 128,
+      format: 'shape',
+    });
+  });
+
+  it('coerces threshold and accepts optional params', () => {
+    expect(
+      traceRequestSchema.parse({
+        url: 'https://example.com/a.png',
+        mode: 'bw',
+        threshold: '200',
+        format: 'svg',
+        simplify: 1.5,
+        maxColors: '8',
+      }),
+    ).toEqual({
+      url: 'https://example.com/a.png',
+      mode: 'bw',
+      threshold: 200,
+      format: 'svg',
+      simplify: 1.5,
+      maxColors: 8,
+    });
+  });
+
+  it('rejects an invalid url', () => {
+    expect(traceRequestSchema.safeParse({ url: 'not-a-url' }).success).toBe(
+      false,
+    );
+  });
+
+  it('rejects an unknown mode or format', () => {
+    expect(
+      traceRequestSchema.safeParse({
+        url: 'https://example.com/a.png',
+        mode: 'nope',
+      }).success,
+    ).toBe(false);
+    expect(
+      traceRequestSchema.safeParse({
+        url: 'https://example.com/a.png',
+        format: 'nope',
+      }).success,
+    ).toBe(false);
+  });
 });