v0.6.0

Changelog

• a124abf feat: cortex migrate — move a legacy ~/.cortex into the XDG dirs
• ffdc344 feat: cortex rm — permanent session delete (terminal-only, --force gated)
• 9084cf6 feat: cortex_archive / cortex_unarchive MCP tools
• 73d3ad6 fix: cortex migrate is all-or-nothing (pre-release review)
• ffbb2e3 refactor: retire deprecated config.AgentDir alias