Plugin cache drops execute permission on hook scripts (unknown/ directory)

Description

Plugin hook scripts in the unknown/ cache directory are written without the execute bit, causing a "Permission denied" error on every stop hook invocation.

Steps to Reproduce

1. Install a plugin that registers a shell script hook (e.g., ralph-loop from claude-plugins-official)
2. Use Claude Code normally — the stop hook fires on every response
3. Observe the error:

Stop hook error: Failed with non-blocking status code: /bin/sh:
/Users/<user>/.claude/plugins/cache/claude-plugins-official/ralph-loop/unknown/hooks/stop-hook.sh: Permission denied

Details

• The plugin cache directory at ~/.claude/plugins/cache/<org>/<plugin>/ contains multiple versioned subdirectories (e.g., 61c0597779bd/, 79caa0d824ac/) plus an unknown/ directory used as a fallback when the plugin version can't be resolved.
• The versioned directories correctly preserve chmod +x on .sh files.
• The unknown/ directory creates files with -rw-r--r-- (644) instead of -rwxr-xr-x (755).
• Manually running chmod +x on the file fixes it temporarily, but the unknown/ directory gets regenerated (losing the fix).

Expected Behavior

Hook scripts in the unknown/ cache directory should be written with the execute bit set, matching the behavior of versioned cache directories.

Environment

• macOS (Darwin 25.2.0)
• Claude Code CLI
• Plugin: ralph-loop from claude-plugins-official