feat: print MCP client config

[haasonsaas]

Summary

• add agentd mcp config to emit a Claude/Codex-style MCP client config snippet
• support explicit command paths and server names for installed app wiring
• document the setup helper and cover parser/config encoding in tests

Verification

• swift test
• swift build -Xswiftc -warnings-as-errors
• xcrun swift-format lint --strict --recursive Sources Tests Package.swift
• git diff --check
• .build/debug/agentd mcp config --command /usr/local/bin/agentd

[cursor]

PR Summary

Low Risk
Low risk: adds a new diagnostic subcommand that only prints JSON to stdout and does not change capture, auth, or network behavior.

Overview
Adds agentd mcp config to print a Claude/Codex-style MCP client configuration JSON for wiring the local agentd stdio MCP server.

The new subcommand supports --command (explicit agentd executable path) and --server-name, defaults the command to the current executable path, and updates help/docs plus unit tests to cover parsing and JSON encoding.

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