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/assemblyai.yaml

@@ -0,0 +1,21 @@
+format_version: 1
+name: assemblyai
+display_name: AssemblyAI
+tier: 3
+last_verified: "2026-04-05"
+keywords:
+  - "assemblyai"
+  - "ASSEMBLYAI_API_KEY"
+  - "api.assemblyai.com"
+  - "assembly.ai"
+patterns:
+  - regex: '[a-f0-9]{32}'
+    entropy_min: 4.0
+    confidence: low
+verify:
+  method: GET
+  url: https://api.assemblyai.com/v2/transcript
+  headers:
+    authorization: "{KEY}"
+  valid_status: [200]
+  invalid_status: [401, 403]