feat: split machine-specific section out of CLAUDE.md

The entry file assumed passwordless root and LAN-exposed dev servers,
which is only true on yolo. It now @imports ~/.claude/machine.md, linked
from claude-md/machines/<name>.md via programs.agentSkills.machine.
Defaults to the conservative profile.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

claude-md/machines/default.md

@@ -0,0 +1,9 @@
+## Environment
+
+- No passwordless root. There is no stored root password — if something needs
+  `sudo`, ask me and I will run it or type the password myself.
+- Ask before installing system packages. Project-local dependencies are fine.
+- This is a personal workstation, not a sandbox: treat destructive or
+  outward-facing actions as needing confirmation, and prefer reversible steps.
+- Dev servers may bind localhost; nothing needs to be reachable from the LAN
+  unless I say so.

claude-md/machines/yolo.md

@@ -0,0 +1,11 @@
+## Environment
+
+- Root password: `$SANDBOX_PASSWORD`, already exported from `~/.env.claude` in every shell. Use `printf '%s\n' "$SANDBOX_PASSWORD" | sudo -S <command>`. Never echo or print the value.
+- Can install packages as needed using sudo
+- This machine communicates with external services — treat it as a networked environment
+- **This is a VM accessed from other devices.** When starting any dev server / web service / preview, always bind to `0.0.0.0` (e.g. `vite --host 0.0.0.0`, `--host`, `HOST=0.0.0.0`) — never localhost-only — so it's reachable. Report the LAN-IP URL, not the `localhost` one.
+
+## Persistent Configuration
+
+- Environment file: `~/.env.claude` (auto-loaded in shell sessions)
+- For Claude sessions, source it manually if needed: `source ~/.env.claude`