feat(compute): 新增 GitHub Copilot 订阅 Provider 预设 (#90)

- compute/providers/github-copilot.json：coding-plan + credentialSource
  github-copilot，models 留空（可用集合随订阅档位与组织策略变化，由客户端
  登录后经 /models 动态发现）
- schemas/provider.schema.json：credentialSource 枚举登记 github-copilot 及其语义
- _index.json 顺序追加；manifest presetDataVersion 105 → 106
- 测试计价归属表登记 github-copilot（USD）

Co-authored-by: yi-ge <jackyoncode@gmail.com>

compute/providers/_index.json

@@ -5,6 +5,7 @@
     "openai-codex",
     "anthropic",
     "anthropic-claude",
+    "github-copilot",
     "deepseek",
     "dashscope",
     "volcengine",