feat: add profile rename command

[njbrake]

Summary

• Adds aoe profile rename <old_name> <new_name> CLI command (with mv alias) to rename profiles
• Renames the profile directory on disk, moving all sessions, groups, and config with it
• Automatically updates the default profile setting if the renamed profile was the default
• Validates new name (non-empty, no path separators, doesn't already exist)

Fixes #328

Test plan

• 7 new integration tests covering: basic rename, default profile update, non-default preservation, rename to existing name, nonexistent profile, empty name, path separators
• Full test suite passes (692 unit tests + 14 profile management tests + all integration tests)
• cargo fmt clean
• cargo clippy clean
• Manual: aoe profile create foo && aoe profile rename foo bar && aoe profile list
• Manual: set default profile, rename it, verify default updated

🤖 Generated with Claude Code

[github-actions]

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