feat(02-04): add Lepton, Modal, Cerebrium, Novita provider YAMLs

- Lepton AI generic-format with keyword anchors
- Modal dual token (token_id ak-, token_secret as-) medium confidence
- Cerebrium generic-format with keyword anchors
- NovitaAI with live verify endpoint (api.novita.ai/v3/openai/models)
- Dual-located in providers/ and pkg/providers/definitions/

providers/lepton.yaml

@@ -0,0 +1,20 @@
+format_version: 1
+name: lepton
+display_name: Lepton AI (DGX Cloud Lepton)
+tier: 2
+last_verified: "2026-04-05"
+keywords:
+  - "lepton"
+  - "lepton.ai"
+  - "LEPTON_API_TOKEN"
+  - "dgx-cloud-lepton"
+patterns:
+  - regex: '[A-Za-z0-9]{32,}'
+    entropy_min: 4.0
+    confidence: low
+verify:
+  method: GET
+  url: ""
+  headers: {}
+  valid_status: []
+  invalid_status: []