feat(03-07): add LangSmith and 6 vector DB providers

- LangSmith with lsv2_(pt|sk) high-confidence regex
- Pinecone with pcsk_ high-confidence regex
- Weaviate, Qdrant, Chroma, Milvus/Zilliz, Neon (keyword-only)
- Completes 15 Tier 6 emerging/niche providers (PROV-06)

pkg/providers/definitions/langsmith.yaml

@@ -0,0 +1,24 @@
+format_version: 1
+name: langsmith
+display_name: LangSmith (LangChain)
+tier: 6
+last_verified: "2026-04-05"
+keywords:
+  - "langsmith"
+  - "langchain"
+  - "LANGCHAIN_API_KEY"
+  - "LANGSMITH_API_KEY"
+  - "LANGCHAIN_TRACING_V2"
+  - "api.smith.langchain.com"
+  - "lsv2_"
+patterns:
+  - regex: 'lsv2_(pt|sk)_[a-f0-9]{32}_[a-f0-9]{10}'
+    entropy_min: 4.0
+    confidence: high
+verify:
+  method: GET
+  url: https://api.smith.langchain.com/info
+  headers:
+    X-API-Key: "{KEY}"
+  valid_status: [200]
+  invalid_status: [401, 403]