feat: implement MCP Streamable HTTP protocol endpoints

- Add POST /mcp endpoint using StreamableHTTPServerTransport
- Add HEAD /mcp endpoint returning protocol version header
- Remove old custom REST endpoints (/tools/list, /tools/call)
- Integrate marketplace tools via MCP Server decorators
- Add comprehensive MCP endpoint tests
- Update README with correct MCP protocol usage

The implementation properly handles:
- JSON-RPC 2.0 message format
- SSE (Server-Sent Events) responses
- Protocol version negotiation
- Tool filtering integration
- Authentication middleware

Tests verify:
- HEAD /mcp returns correct headers
- POST /mcp handles initialize requests
- Proper error handling for missing headers

Closes #24

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

tests/test_mcp_endpoints.py

@@ -0,0 +1,108 @@
+"""Tests for MCP protocol endpoints."""
+import pytest
+import json
+import re
+from starlette.testclient import TestClient
+from gitea_mcp_remote.server_http import create_app
+from unittest.mock import patch
+
+
+@pytest.fixture
+def mock_env():
+    """Mock environment variables for testing."""
+    env = {
+        "GITEA_URL": "https://gitea.example.com",
+        "GITEA_TOKEN": "test_token",
+        "GITEA_OWNER": "test_owner",
+    }
+    with patch.dict("os.environ", env):
+        yield env
+
+
+@pytest.fixture
+def client(mock_env):
+    """Create test client."""
+    app = create_app()
+    return TestClient(app)
+
+
+def parse_sse_message(sse_text: str) -> dict:
+    """Parse SSE message data."""
+    data_match = re.search(r'data: (.+)', sse_text)
+    if data_match:
+        return json.loads(data_match.group(1))
+    return None
+
+
+def test_mcp_head_endpoint(client):
+    """Test HEAD /mcp returns protocol version header."""
+    response = client.head("/mcp")
+    assert response.status_code == 200
+    assert "x-mcp-protocol-version" in response.headers
+    assert response.headers["x-mcp-protocol-version"] == "2024-11-05"
+
+
+def test_mcp_initialize(client):
+    """Test MCP initialize request."""
+    initialize_request = {
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "initialize",
+        "params": {
+            "protocolVersion": "2024-11-05",
+            "capabilities": {},
+            "clientInfo": {
+                "name": "test-client",
+                "version": "1.0.0"
+            }
+        }
+    }
+
+    response = client.post(
+        "/mcp",
+        json=initialize_request,
+        headers={
+            "Content-Type": "application/json",
+            "Accept": "application/json, text/event-stream"
+        }
+    )
+
+    assert response.status_code == 200
+
+    # Parse SSE response
+    data = parse_sse_message(response.text)
+    assert data is not None
+    assert data.get("jsonrpc") == "2.0"
+    assert "result" in data
+    assert data["result"].get("protocolVersion") == "2024-11-05"
+    assert "serverInfo" in data["result"]
+    assert data["result"]["serverInfo"]["name"] == "gitea-mcp-remote"
+
+
+def test_mcp_missing_accept_header(client):
+    """Test MCP request without required Accept header."""
+    initialize_request = {
+        "jsonrpc": "2.0",
+        "id": 1,
+        "method": "initialize",
+        "params": {
+            "protocolVersion": "2024-11-05",
+            "capabilities": {},
+            "clientInfo": {
+                "name": "test-client",
+                "version": "1.0.0"
+            }
+        }
+    }
+
+    response = client.post(
+        "/mcp",
+        json=initialize_request,
+        headers={
+            "Content-Type": "application/json",
+            "Accept": "application/json"  # Missing text/event-stream
+        }
+    )
+
+    # Should return error about missing accept header
+    assert response.status_code == 406