refactor: slim backend routers to ≤500 lines

- tool_instances.py: 2108 → 496 lines
- git_repositories.py: 1422 → 500 lines
- config_profiles.py: 474 → 300 lines (already committed)

Extract business logic into services:
- services/tool/instance_service.py
- services/git/operations.py
- services/config/crud_service.py

Quality gates: py_compile pass on all files

apps/api/src/schemas/project/git_repository.py

@@ -45,3 +45,91 @@ class GitRepositoryResponse(BaseModel):
 
 class UpdateSSHKeyRequest(BaseModel):
     ssh_key_id: str | None = None
+
+
+class FileListResponse(BaseModel):
+    path: str
+    branch: str
+    entries: list[dict]
+
+
+class FileContentResponse(BaseModel):
+    path: str
+    branch: str
+    content: str
+    size: int
+    encoding: str
+    language: str | None
+    is_binary: bool
+    last_commit: dict | None
+
+
+class BranchesResponse(BaseModel):
+    branches: list[dict]
+    default_branch: str
+
+
+class FileUpdateRequest(BaseModel):
+    path: str
+    branch: str
+    content: str
+    commit_message: str
+
+
+class FileUpdateResponse(BaseModel):
+    commit_hash: str
+    message: str
+    branch: str
+
+
+class StatusResponse(BaseModel):
+    branch: str
+    modified: list[str]
+    added: list[str]
+    deleted: list[str]
+    untracked: list[str]
+    renamed: list[str]
+    ahead: int
+    behind: int
+
+
+class BranchCreateRequest(BaseModel):
+    name: str
+    base_branch: str = "HEAD"
+
+
+class CheckoutRequest(BaseModel):
+    branch: str
+
+
+class CommitRequest(BaseModel):
+    message: str
+    files: list[str] | None = None
+
+
+class CommitResponse(BaseModel):
+    commit_hash: str
+    message: str
+
+
+class FetchResponse(BaseModel):
+    message: str
+
+
+class PullResponse(BaseModel):
+    message: str
+
+
+class PushResponse(BaseModel):
+    message: str
+
+
+class MergeRequest(BaseModel):
+    source_branch: str
+    target_branch: str | None = None
+    message: str | None = None
+
+
+class MergeResponse(BaseModel):
+    commit_hash: str
+    message: str