fix: hooks degrade gracefully when node is not on PATH (#57)

Claude Code runs hooks via a non-interactive /bin/sh. On setups where node
isn't on that shell's PATH (Nix/nix-darwin, nvm, fnm), every prompt errored
with "/bin/sh: node: command not found". Guard each hook command so it runs
node only when present and exits 0 otherwise, no more per-prompt noise. The
slash-command skills are unaffected; only the always-on activation needs node.
Document the requirement in the README install section.

Closes #51.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: DietrichGebert

README.md

@@ -71,6 +71,8 @@ Lazy, not negligent: trust-boundary validation, data-loss handling, security, an
 
 The most effort ponytail will ever ask of you:
 
+The Claude Code and Codex plugins run two tiny Node.js lifecycle hooks, so `node` needs to be on your PATH (note for Nix/nvm users: it must be on the non-interactive shell's PATH). If it isn't, the skills still work, the always-on activation just stays quiet instead of erroring on every prompt.
+
 ### Claude Code
 
 ```

hooks/hooks.json

@@ -6,8 +6,8 @@
         "hooks": [
           {
             "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/ponytail-activate.js\"",
-            "commandWindows": "node \"$env:CLAUDE_PLUGIN_ROOT\\hooks\\ponytail-activate.js\"",
+            "command": "command -v node >/dev/null 2>&1 && node \"${CLAUDE_PLUGIN_ROOT}/hooks/ponytail-activate.js\" || exit 0",
+            "commandWindows": "if (Get-Command node -ErrorAction SilentlyContinue) { node \"$env:CLAUDE_PLUGIN_ROOT\\hooks\\ponytail-activate.js\" }",
             "timeout": 5,
             "statusMessage": "Loading ponytail mode..."
           }
@@ -19,8 +19,8 @@
         "hooks": [
           {
             "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/ponytail-mode-tracker.js\"",
-            "commandWindows": "node \"$env:CLAUDE_PLUGIN_ROOT\\hooks\\ponytail-mode-tracker.js\"",
+            "command": "command -v node >/dev/null 2>&1 && node \"${CLAUDE_PLUGIN_ROOT}/hooks/ponytail-mode-tracker.js\" || exit 0",
+            "commandWindows": "if (Get-Command node -ErrorAction SilentlyContinue) { node \"$env:CLAUDE_PLUGIN_ROOT\\hooks\\ponytail-mode-tracker.js\" }",
             "timeout": 5,
             "statusMessage": "Tracking ponytail mode..."
           }