feat: add early v4 detection for improved update flow

- Now detects existing v4 installations immediately after directory prompt
- Offers update option upfront for existing v4 installations
- If user declines update, continues with normal installation flow
- Added 'update' install type handling in installer
- Improves user experience by streamlining the update process

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

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

tools/installer/lib/installer.js

@@ -102,6 +102,17 @@ class Installer {
         spinner.start("Analyzing installation directory...");
       }
 
+      // If this is an update request from early detection, handle it directly
+      if (config.installType === 'update') {
+        const state = await this.detectInstallationState(installDir);
+        if (state.type === 'v4_existing') {
+          return await this.performUpdate(config, installDir, state.manifest, spinner);
+        } else {
+          spinner.fail('No existing v4 installation found to update');
+          throw new Error('No existing v4 installation found');
+        }
+      }
+
       // Detect current state
       const state = await this.detectInstallationState(installDir);