feat: support MCP readOnlyHint annotation in plan mode (#1826)

[echoVic]

Summary

MCP tools annotated with readOnlyHint: true are now allowed to execute in plan mode without being blocked.

Problem

Previously, all MCP tools were assigned Kind.Other and required user confirmation. In plan mode, any tool requiring confirmation is blocked with:

"Plan mode blocked a non-read-only tool call."

This means MCP tools that are explicitly marked as read-only (via the MCP readOnlyHint annotation) cannot be used in plan mode, even though they are safe to execute. Users cannot gather information from MCP sources while in plan mode.

Solution

1. Fetch tool annotations — During MCP tool discovery, call mcpClient.listTools() to retrieve the raw tool list with annotations (which mcpToTool's functionDeclarations conversion does not preserve).
2. Pass annotations through — Store McpToolAnnotations in both DiscoveredMCPTool and DiscoveredMCPToolInvocation.
3. Set correct Kind — Tools with readOnlyHint: true get Kind.Read instead of Kind.Other.
4. Skip confirmation — In shouldConfirmExecute(), tools with readOnlyHint: true return false (no confirmation needed), so plan mode does not block them.

Changes

• packages/core/src/tools/mcp-tool.ts: Add McpToolAnnotations interface, accept annotations in constructors, use Kind.Read for read-only tools, skip confirmation for readOnlyHint: true
• packages/core/src/tools/mcp-client.ts: Fetch annotations via mcpClient.listTools() during discovery, pass to DiscoveredMCPTool

Testing

• MCP tools with readOnlyHint: true annotation now execute in plan mode without being blocked
• MCP tools without annotations or with readOnlyHint: false behave as before (require confirmation, blocked in plan mode)
• If listTools() fails, discovery proceeds gracefully without annotations (non-breaking)

Fixes #1826

[LaZzyMan]

LGTM！