feat(03-02): add search and embeddings Tier 3 providers

- Perplexity (pplx- prefix, high confidence)
- You.com (keyword-only)
- Voyage AI (pa- prefix, medium confidence)
- Jina AI (jina_ prefix, high confidence)
- Unstructured.io (keyword-only)
- AssemblyAI (hex32, low confidence)

providers/you.yaml

@@ -0,0 +1,17 @@
+format_version: 1
+name: you
+display_name: You.com
+tier: 3
+last_verified: "2026-04-05"
+keywords:
+  - "you.com"
+  - "YDC_API_KEY"
+  - "YOU_API_KEY"
+  - "api.ydc-index.io"
+verify:
+  method: GET
+  url: https://api.ydc-index.io/search
+  headers:
+    X-API-Key: "{KEY}"
+  valid_status: [200, 400]
+  invalid_status: [401, 403]