feat: MCP Server plugin (Task 5.16) - expose LeoCRM tools to external AI clients

- New plugin app/plugins/builtins/mcp_server/ with 9 MCP tools
- Tools: search_contacts, get_contact, create_contact, list_calendar_entries,
  create_calendar_entry, list_emails, send_email, list_files, upload_file
- Routes: GET /api/v1/mcp/tools, POST /api/v1/mcp/tools/{name}/execute, GET /api/v1/mcp/config
- API-token auth via session + RBAC (mcp:read, mcp:write)
- Frontend: mcp.ts API client with React Query hooks
- Frontend: SettingsMcp.tsx settings page with tool listing and execution
- i18n: de.json and en.json updated with MCP entries
- Tests: 7 tests covering tool listing, config, execution, auth, schema validation

app/plugins/builtins/mcp_server/routes.py

@@ -0,0 +1,129 @@
+"""MCP Server plugin routes — tool listing, execution, and config."""
+
+from __future__ import annotations
+
+import logging
+import uuid
+from typing import Any
+
+from fastapi import APIRouter, Depends, Header, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.db import get_db
+from app.deps import get_current_user, require_permission
+from app.plugins.builtins.mcp_server.schemas import (
+    McpServerConfig,
+    McpToolDefinition,
+    McpToolExecuteRequest,
+    McpToolExecuteResponse,
+    McpToolListResponse,
+)
+from app.plugins.builtins.mcp_server.tool_definitions import (
+    TOOL_DEFINITIONS,
+    TOOL_HANDLERS,
+    get_all_tool_names,
+    get_tool_definition,
+)
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/api/v1/mcp", tags=["mcp-server"])
+
+
+async def _get_mcp_context(
+    current_user: dict[str, Any] = Depends(get_current_user),
+) -> dict[str, Any]:
+    """Build MCP execution context from authenticated user."""
+    return {
+        "tenant_id": current_user.get("tenant_id"),
+        "user_id": current_user.get("user_id"),
+        "role": current_user.get("role"),
+        "permissions": current_user.get("permissions", []),
+    }
+
+
+@router.get("/tools", response_model=McpToolListResponse)
+async def list_mcp_tools(
+    current_user: dict[str, Any] = Depends(require_permission("mcp:read")),
+) -> McpToolListResponse:
+    """List all available MCP tools with their schemas."""
+    return McpToolListResponse(
+        tools=TOOL_DEFINITIONS,
+        count=len(TOOL_DEFINITIONS),
+    )
+
+
+@router.post("/tools/{tool_name}/execute", response_model=McpToolExecuteResponse)
+async def execute_mcp_tool(
+    tool_name: str,
+    request: McpToolExecuteRequest,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict[str, Any] = Depends(get_current_user),
+) -> McpToolExecuteResponse:
+    """Execute an MCP tool by name with provided arguments.
+
+    Requires mcp:read for read tools, mcp:write for write tools.
+    """
+    tool_def = get_tool_definition(tool_name)
+    if not tool_def:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail={"detail": f"MCP tool '{tool_name}' not found", "code": "tool_not_found"},
+        )
+
+    # Check permission based on tool category
+    required_perm = tool_def.required_permission or "mcp:read"
+    from app.core.permissions import check_permission
+
+    if not current_user.get("is_system_admin") and not check_permission(current_user, required_perm):
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail={"detail": f"Permission '{required_perm}' required", "code": "forbidden"},
+        )
+
+    handler = TOOL_HANDLERS.get(tool_name)
+    if not handler:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail={"detail": f"Handler for '{tool_name}' not implemented", "code": "handler_missing"},
+        )
+
+    context = {
+        "tenant_id": current_user.get("tenant_id"),
+        "user_id": current_user.get("user_id"),
+        "role": current_user.get("role"),
+        "permissions": current_user.get("permissions", []),
+    }
+
+    try:
+        result = await handler(db, request.arguments, context)
+        await db.commit()
+        return McpToolExecuteResponse(
+            tool=tool_name,
+            success="error" not in result,
+            result=result,
+            error=result.get("error"),
+        )
+    except Exception as exc:
+        logger.exception("MCP tool execution failed: %s", tool_name)
+        await db.rollback()
+        return McpToolExecuteResponse(
+            tool=tool_name,
+            success=False,
+            error=str(exc),
+        )
+
+
+@router.get("/config", response_model=McpServerConfig)
+async def get_mcp_config(
+    current_user: dict[str, Any] = Depends(require_permission("mcp:read")),
+) -> McpServerConfig:
+    """Get MCP server configuration for external clients."""
+    return McpServerConfig(
+        server_name="LeoCRM",
+        server_version="1.0.0",
+        protocol_version="2024-11-05",
+        base_url="/api/v1/mcp",
+        auth_method="api-token",
+        available_tools=get_all_tool_names(),
+    )