feat(02-02): add Mistral, Inflection, AI21 provider YAMLs

- 3 Tier 1 low-confidence providers with keyword anchoring
- Dual-located in providers/ and pkg/providers/definitions/
- Tier 1 total now at 12/12 providers

pkg/providers/definitions/inflection.yaml

@@ -0,0 +1,21 @@
+format_version: 1
+name: inflection
+display_name: Inflection AI (Pi)
+tier: 1
+last_verified: "2026-04-05"
+keywords:
+  - "inflection"
+  - "pi_api"
+  - "PI_API_KEY"
+  - "INFLECTION_API_KEY"
+  - "inflection.ai"
+patterns:
+  - regex: '[A-Za-z0-9_\-]{40,}'
+    entropy_min: 4.0
+    confidence: low
+verify:
+  method: GET
+  url: ""
+  headers: {}
+  valid_status: []
+  invalid_status: []