v0.6.4: squidbrake doctor

• squidbrake doctor: one command that checks everything end to end and says what to fix: the version, the dashboard your agents' hooks use, their key, and for every agent on the computer whether it's connected, whether its hook really runs (a harmless echo sent the way the agent sends it), Codex trust, and whether the agent has actually called the hook since it was connected. For Cursor it also shows the Cursor version and errors from Cursor's own hooks log. The start-page installers run it at the end.
• The hooks note each call (which agent, which hook event, when; never the command, file or key) in ~/.squidbrake/hooks.log, so doctor can tell "connected but never used" from "working".
• Shell guard: squidbrake shell-guard install --shell bash|zsh|powershell prints a snippet that checks lines you type or paste into your own terminal: catastrophic ones are blocked, irreversible ones ask first. Thanks @vinayakpotdar79 (#61).