feat(03-02): add voice and image/video Tier 3 providers

- Deepgram (hex40, low confidence)
- ElevenLabs (hex32, XI_API_KEY header)
- Stability AI (sk- prefix, medium confidence)
- Runway (keyword-only)
- Midjourney (keyword-only, no official API)

Completes PROV-03: 12 Tier 3 Specialized providers (with pre-existing huggingface).

providers/midjourney.yaml

@@ -0,0 +1,17 @@
+format_version: 1
+name: midjourney
+display_name: Midjourney
+tier: 3
+last_verified: "2026-04-05"
+keywords:
+  - "midjourney"
+  - "MIDJOURNEY_API_KEY"
+  - "MJ_API_KEY"
+  - "midjourney.com"
+  - "useapi.net"
+verify:
+  method: GET
+  url: ""
+  headers: {}
+  valid_status: []
+  invalid_status: []