Plugin install silently fails when folder/symlink with same name exists

Description

When running /plugin install <plugin-name>@<marketplace>, if a folder or symlink with the same name already exists in ~/.claude/plugins/, the command returns no output and silently does nothing.

Steps to Reproduce

1. Create a symlink in plugins directory:

``bash
ln -s /some/path ~/.claude/plugins/my-plugin
``

1. Add a marketplace containing a plugin named my-plugin:

``bash
/plugin marketplace add someuser/marketplace-repo
``

1. Try to install:

``bash
/plugin install my-plugin@marketplace-name
``

1. Result: No output, no error, nothing happens

Expected Behavior

The command should output a clear message, such as:

Error: "my-plugin" already exists at ~/.claude/plugins/my-plugin (symlink)
Use --force to replace, or remove it manually first.

Actual Behavior

Command completes with no output, leaving user confused about whether installation succeeded or failed.

Environment

• Claude Code CLI
• macOS

Suggested Fix

1. Detect existing folders/symlinks before install
2. Output clear error message explaining the conflict
3. Optionally support --force flag to overwrite

---
🤖 Filed via Claude Code