fix: auto-login after signup and context-aware token clearing

This fixes the "Authorization header required for API calls" error during
vendor onboarding after signup.

Changes:
- Generate JWT access token on signup completion
- Set vendor_token cookie for page navigation
- Return access_token in signup response for localStorage
- Store vendor_token in localStorage after signup completion
- Make clearTokens() context-aware to prevent cross-portal interference
- Fix vendor logout to not clear admin/customer tokens

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

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

static/vendor/js/init-alpine.js

@@ -106,12 +106,13 @@ function data() {
             } catch (error) {
                 console.error('⚠️ Logout API error (continuing anyway):', error);
             } finally {
-                // Clear all tokens and data
-                console.log('🧹 Clearing tokens...');
+                // Clear vendor tokens only (not admin or customer tokens)
+                console.log('🧹 Clearing vendor tokens...');
                 localStorage.removeItem('vendor_token');
+                localStorage.removeItem('vendor_user');
                 localStorage.removeItem('currentUser');
                 localStorage.removeItem('vendorCode');
-                localStorage.clear(); // Clear everything to be safe
+                // Note: Do NOT use localStorage.clear() - it would clear admin/customer tokens too
 
                 console.log('🔄 Redirecting to login...');
                 window.location.href = `/vendor/${this.vendorCode}/login`;