feat(03-04): add GitHub Copilot, Cursor, Tabnine, Codeium, Sourcegraph providers

- GitHub Copilot with ghu_/gho_ token patterns
- Sourcegraph Cody with documented sgp_ high-confidence pattern
- Cursor, Tabnine, Codeium as keyword-only (no documented formats)

pkg/providers/definitions/github-copilot.yaml

@@ -0,0 +1,25 @@
+format_version: 1
+name: github-copilot
+display_name: GitHub Copilot
+tier: 7
+last_verified: "2026-04-05"
+keywords:
+  - "copilot"
+  - "github-copilot"
+  - "GITHUB_COPILOT_TOKEN"
+  - "api.githubcopilot.com"
+  - "copilot-internal"
+patterns:
+  - regex: 'ghu_[A-Za-z0-9]{36}'
+    entropy_min: 4.0
+    confidence: medium
+  - regex: 'gho_[A-Za-z0-9]{36}'
+    entropy_min: 4.0
+    confidence: medium
+verify:
+  method: GET
+  url: https://api.github.com/user
+  headers:
+    Authorization: "token {KEY}"
+  valid_status: [200]
+  invalid_status: [401, 403]