Remove unstable public APIs from SDK (#151)

Hide hooks, tool permission callbacks, and SDK MCP server APIs from
public interface while keeping implementation code intact. These
features are not yet stable and should not be documented or exposed to
users.

Changes:
- Remove hook-related exports (HookCallback, HookContext, HookMatcher)
from __all__
- Remove tool permission exports (CanUseTool, ToolPermissionContext)
from __all__
- Remove SDK MCP exports (tool, create_sdk_mcp_server, SdkMcpTool) from
__all__
- Delete examples using unstable APIs (tool_permission_callback.py,
mcp_calculator.py)
- Remove SDK MCP server documentation from README

🤖 Generated with [Claude Code](https://claude.ai/code)

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/claude_code_sdk/__init__.py

@@ -16,12 +16,8 @@ from .client import ClaudeSDKClient
 from .query import query
 from .types import (
     AssistantMessage,
-    CanUseTool,
     ClaudeCodeOptions,
     ContentBlock,
-    HookCallback,
-    HookContext,
-    HookMatcher,
     McpSdkServerConfig,
     McpServerConfig,
     Message,
@@ -34,7 +30,6 @@ from .types import (
     SystemMessage,
     TextBlock,
     ThinkingBlock,
-    ToolPermissionContext,
     ToolResultBlock,
     ToolUseBlock,
     UserMessage,
@@ -297,20 +292,11 @@ __all__ = [
     "ToolUseBlock",
     "ToolResultBlock",
     "ContentBlock",
-    # Tool callbacks
-    "CanUseTool",
-    "ToolPermissionContext",
+    # Permission results (keep these as they may be used by internal callbacks)
     "PermissionResult",
     "PermissionResultAllow",
     "PermissionResultDeny",
     "PermissionUpdate",
-    "HookCallback",
-    "HookContext",
-    "HookMatcher",
-    # MCP Server Support
-    "create_sdk_mcp_server",
-    "tool",
-    "SdkMcpTool",
     # Errors
     "ClaudeSDKError",
     "CLIConnectionError",