feat(tools): implement issue operations - Closes #3

Implement Gitea issue operations tools with the following features:
- gitea_list_issues: List issues with filters (state, labels, milestone)
- gitea_get_issue: Get single issue by number
- gitea_create_issue: Create new issue with title, body, labels, milestone
- gitea_update_issue: Update issue state, title, body, labels, assignees

Files added:
- src/gitea_mcp/tools/issues.py: Issue operation tool handlers

Files modified:
- src/gitea_mcp/server.py: Register issue tools in MCP server
- src/gitea_mcp/tools/__init__.py: Export issue tool functions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/gitea_mcp/server.py

@@ -9,6 +9,7 @@ from mcp.types import Tool, TextContent
 from . import __version__
 from .auth import AuthConfig
 from .client import GiteaClient, GiteaClientError
+from .tools import get_issue_tools, handle_issue_tool
 
 
 # Global client instance
@@ -35,10 +36,13 @@ async def serve() -> None:
         """List available MCP tools.
 
         Returns:
-            list: Available tools (placeholder for future implementation).
+            list: Available tools including issue operations.
         """
-        # Placeholder tools - will be implemented in issues #3, #4, #5
-        return [
+        # Get issue tools
+        tools = get_issue_tools()
+
+        # Placeholder for future tools (PR tools, etc.)
+        tools.extend([
             Tool(
                 name="list_repositories",
                 description="List repositories in an organization (coming soon)",
@@ -53,32 +57,6 @@ async def serve() -> None:
                     "required": ["org"],
                 },
             ),
-            Tool(
-                name="create_issue",
-                description="Create a new issue in a repository (coming soon)",
-                inputSchema={
-                    "type": "object",
-                    "properties": {
-                        "owner": {
-                            "type": "string",
-                            "description": "Repository owner",
-                        },
-                        "repo": {
-                            "type": "string",
-                            "description": "Repository name",
-                        },
-                        "title": {
-                            "type": "string",
-                            "description": "Issue title",
-                        },
-                        "body": {
-                            "type": "string",
-                            "description": "Issue body",
-                        },
-                    },
-                    "required": ["owner", "repo", "title"],
-                },
-            ),
             Tool(
                 name="create_pull_request",
                 description="Create a new pull request (coming soon)",
@@ -109,7 +87,9 @@ async def serve() -> None:
                     "required": ["owner", "repo", "title", "head", "base"],
                 },
             ),
-        ]
+        ])
+
+        return tools
 
     @server.call_tool()
     async def call_tool(name: str, arguments: dict) -> list[TextContent]:
@@ -122,11 +102,17 @@ async def serve() -> None:
         Returns:
             list: Tool response.
         """
-        # Placeholder implementation - actual tools will be implemented in future issues
+        # Handle issue tools
+        if name.startswith("gitea_") and any(
+            name.endswith(suffix) for suffix in ["_issues", "_issue"]
+        ):
+            return await handle_issue_tool(name, arguments, gitea_client)
+
+        # Placeholder for other tools
         return [
             TextContent(
                 type="text",
-                text=f"Tool '{name}' is not yet implemented. Coming soon in issues #3, #4, #5.",
+                text=f"Tool '{name}' is not yet implemented.",
             )
         ]