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/perplexity.yaml

@@ -0,0 +1,21 @@
+format_version: 1
+name: perplexity
+display_name: Perplexity AI
+tier: 3
+last_verified: "2026-04-05"
+keywords:
+  - "perplexity"
+  - "PERPLEXITY_API_KEY"
+  - "pplx-"
+  - "api.perplexity.ai"
+patterns:
+  - regex: 'pplx-[A-Za-z0-9]{48,}'
+    entropy_min: 4.0
+    confidence: high
+verify:
+  method: POST
+  url: https://api.perplexity.ai/chat/completions
+  headers:
+    Authorization: "Bearer {KEY}"
+  valid_status: [200, 400]
+  invalid_status: [401, 403]