fix(windows): restore Bun auto-installation in smart-install.js

CRITICAL FIX: v7.1.0 Bun auto-install broken on Windows 11

Problem:
- hooks.json calls `bun smart-install.js` but if Bun isn't installed,
  command fails immediately with "bun is not recognized"
- smart-install.js never runs, so Bun never gets installed
- Chicken-and-egg problem

Root Cause:
- v7.1.0 removed Bun/uv auto-installation logic from smart-install.js
- Assumed Bun would already be available
- Breaks fresh installations on all platforms

Solution:
1. Changed SessionStart hook to use `node` for smart-install.js
   (Node.js always available in Claude Code)
2. Restored Bun auto-installation logic:
   - isBunInstalled() - check if Bun is in PATH
   - installBun() - auto-install via PowerShell (Windows) or curl (Unix/macOS)
   - Also restored uv auto-installation for Chroma

After Fix:
- smart-install.js runs with node (always available)
- Detects if Bun is missing and auto-installs it
- Subsequent hooks use bun successfully
- Works on fresh Windows installations

Fixes: User report from Discord - Windows 11 'bun' is not recognized

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

plugin/hooks/hooks.json

@@ -7,7 +7,7 @@
         "hooks": [
           {
             "type": "command",
-            "command": "bun \"${CLAUDE_PLUGIN_ROOT}/scripts/smart-install.js\" && bun \"${CLAUDE_PLUGIN_ROOT}/scripts/context-hook.js\"",
+            "command": "node \"${CLAUDE_PLUGIN_ROOT}/scripts/smart-install.js\" && bun \"${CLAUDE_PLUGIN_ROOT}/scripts/context-hook.js\"",
             "timeout": 300
           },
           {