refactor(git): introduce GitRunError hierarchy, surface non-repo errors, and improve verification queries

* Replace legacy GitError usage with a clearer exception hierarchy:

  * GitBaseError as the common root for all git-related failures
  * GitRunError for subprocess execution failures
  * GitQueryError for read-only query failures
  * GitCommandError for state-changing command failures
  * GitNotRepositoryError to explicitly signal “not a git repository” situations
* Update git runner to detect “not a git repository” stderr and raise GitNotRepositoryError with rich context (cwd, command, stderr)
* Refactor repository verification to use dedicated query helpers instead of ad-hoc subprocess calls:

  * get_remote_head_commit (ls-remote) for pull mode
  * get_head_commit for local mode
  * get_latest_signing_key (%GK) for signature verification
* Add strict vs best-effort behavior in verify_repository:

  * Best-effort collection for reporting (does not block when no verification config exists)
  * Strict retrieval and explicit error messages when verification is configured
  * Clear failure cases when commit/signing key cannot be determined
* Add new unit tests covering:

  * get_latest_signing_key output stripping and error wrapping
  * get_remote_head_commit parsing, empty output, and error wrapping
  * verify_repository success/failure scenarios and “do not swallow GitNotRepositoryError”
* Adjust imports and exception handling across actions/commands/queries to align with GitRunError-based handling while keeping GitNotRepositoryError uncaught for debugging clarity

https://chatgpt.com/share/6943173c-508c-800f-8879-af75d131c79b

tests/unit/pkgmgr/actions/branch/test_drop_branch.py

@@ -2,7 +2,7 @@ import unittest
 from unittest.mock import patch
 
 from pkgmgr.actions.branch.drop_branch import drop_branch
-from pkgmgr.core.git.errors import GitError
+from pkgmgr.core.git.errors import GitRunError
 from pkgmgr.core.git.commands import GitDeleteRemoteBranchError
 
 
@@ -50,7 +50,7 @@ class TestDropBranch(unittest.TestCase):
         delete_local.assert_called_once_with("feature-x", cwd=".", force=False)
         delete_remote.assert_called_once_with("origin", "feature-x", cwd=".")
 
-    @patch("pkgmgr.actions.branch.drop_branch.get_current_branch", side_effect=GitError("fail"))
+    @patch("pkgmgr.actions.branch.drop_branch.get_current_branch", side_effect=GitRunError("fail"))
     def test_drop_branch_errors_if_no_branch_detected(self, _current) -> None:
         with self.assertRaises(RuntimeError):
             drop_branch(None)