refactor: extract focused clients from GiteaClient (Slices 1-6)

- Create gitea/issues_client.py with IssuesClient class (9 methods)
- Create gitea/prs_client.py with PullRequestsClient class (17 methods)
- Create gitea/files_client.py with FilesClient class (4 methods)
- Create gitea/notifications_client.py with NotificationsClient class (2 methods)
- Create gitea/repos_client.py with ReposClient class (2 methods)
- Create gitea/__init__.py to export all client classes
- Remove delegation methods from GiteaClient (now ~70 lines)
- Update all callers to use sub-clients (client.issues, client.prs, etc.)
- Update test files to mock sub-client attributes

GiteaClient is now a facade that provides access to focused sub-clients:
- repos: Repository operations (ReposClient)
- issues: Issue operations (IssuesClient)
- prs: Pull request operations (PullRequestsClient)
- files: File and git ref operations (FilesClient)
- notifications: Notification operations (NotificationsClient)

Refs: #godclass-refactor

core/orchestrator.py

@@ -90,7 +90,9 @@ class AgentOrchestrator:
             f"Polling unread notifications since: {last_checked or 'beginning'}"
         )
 
-        notifications = self._client.list_unread_notifications(since=last_checked)
+        notifications = self._client.notifications.list_unread_notifications(
+            since=last_checked
+        )
 
         if not notifications:
             logger.info("No new notifications found.")
@@ -165,7 +167,9 @@ class AgentOrchestrator:
                     f"Skipping notification {notification_id} for {repo_full_name}#{task_number}. Reason: {reason}"
                 )
                 if notification_id is not None:
-                    self._client.mark_notification_as_read(notification_id)
+                    self._client.notifications.mark_notification_as_read(
+                        notification_id
+                    )
                     logger.info(
                         f"Marked skipped Gitea notification thread {notification_id} as read."
                     )
@@ -174,7 +178,7 @@ class AgentOrchestrator:
             # Route based on decided action
             if notification_tools.action == "PROCESS_ISSUE":
                 try:
-                    issue = self._client.get_issue(owner, repo_name, task_number)
+                    issue = self._client.issues.get_issue(owner, repo_name, task_number)
                     if issue.repository is None:
                         issue = issue.model_copy(
                             update={"repository": RepositoryModel(**repo_info)}
@@ -195,7 +199,9 @@ class AgentOrchestrator:
                     )
             elif notification_tools.action == "PROCESS_PR":
                 try:
-                    pr = self._client.get_pull_request(owner, repo_name, task_number)
+                    pr = self._client.prs.get_pull_request(
+                        owner, repo_name, task_number
+                    )
                     if pr.repository is None:
                         pr = pr.model_copy(
                             update={"repository": RepositoryModel(**repo_info)}
@@ -252,7 +258,9 @@ class AgentOrchestrator:
                     f"Completed {item.task_type} #{item.task_number}: {result[:200]}"
                 )
                 if item.notification_id is not None:
-                    self._client.mark_notification_as_read(item.notification_id)
+                    self._client.notifications.mark_notification_as_read(
+                        item.notification_id
+                    )
                     logger.info(
                         f"Marked Gitea notification thread {item.notification_id} as read."
                     )