Add fs.existsSync() guards to all .js hook registrations in install.js,
matching the pattern already used for .sh hooks (#1817). When hooks/dist/
is missing from the npm package, the copy step produces no files but the
registration step previously ran unconditionally for .js hooks, causing
"PreToolUse:Bash hook error" on every tool invocation.
Each .js hook (check-update, context-monitor, prompt-guard, read-guard,
workflow-guard) now verifies the target file exists before registering
in settings.json, and emits a skip warning when the file is absent.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
