Plugin re-installation sets version to 'unknown' in installed_plugins.json

Description

When re-installing a plugin that has already been installed in project scope, the claude plugin install command records "version": "unknown" in ~/.claude/plugins/installed_plugins.json instead of the actual version.

Steps to Reproduce

1. Install a plugin at project scope:

``bash
cd /path/to/project
claude plugin install github@claude-plugins-official --scope project
``

1. Re-install the same plugin (either via TUI or CLI):

``bash
claude plugin install github@claude-plugins-official --scope project
``

1. Check ~/.claude/plugins/installed_plugins.json

Expected Behavior

The plugin entry should have the correct version (e.g., "f1be96f0fb58" or semantic version like "1.0.0"):

{
  "scope": "project",
  "projectPath": "/path/to/project",
  "installPath": "/Users/.../.claude/plugins/cache/claude-plugins-official/github/f1be96f0fb58",
  "version": "f1be96f0fb58",
  ...
}

Actual Behavior

The plugin entry has "version": "unknown" and the install path also contains unknown:

{
  "scope": "project",
  "projectPath": "/path/to/project",
  "installPath": "/Users/.../.claude/plugins/cache/claude-plugins-official/github/unknown",
  "version": "unknown",
  ...
}

Additional Observations

1. First installation works correctly - Version information is properly recorded on the initial install
2. TUI cannot re-install - The TUI does not allow re-installation of an already installed plugin (it shows as already installed)
3. User scope also affected - Re-installing at user scope has the same issue
4. Workaround exists - Running claude plugin update <plugin-name> corrects the version:

``bash
claude plugin update github@claude-plugins-official
# ✔ Plugin "github" updated from unknown to f1be96f0fb58 for scope user
``

Environment

• Claude Code version: 2.1.2
• OS: macOS (Darwin 25.2.0)

Impact

• Version tracking becomes unreliable after re-installation
• Users may have inconsistent plugin states across projects
• The install path containing unknown may cause issues with cache management

Suggested Fix

The re-installation flow should retrieve the version information from the marketplace metadata before writing to installed_plugins.json, similar to how the initial installation process works.