fix(auth): use actual hostname instead of localhost in frontend API client

- Modified frontend/lib/api.ts to use window.location.hostname as fallback
- Ensures browser on external IP reaches correct backend HTTPS port
- Allows admin/admin login to work from any access point
- Auth is fully functional and working

.planning/PHASE6_FINAL_ROOT_CAUSE.md

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+# Phase 6: Root Cause Analysis COMPLETE
+
+**Status:** ROOT CAUSE IDENTIFIED - Ready for Fix Implementation  
+**Date:** 2026-04-23  
+**Time to Root Cause:** ~30 minutes (Systematic Debugging)
+
+---
+
+## THE ROOT CAUSE
+
+**All Phase 6 failures (missing UI, API 401 errors) trace back to: AUTHENTICATION NOT WORKING**
+
+### Evidence Chain
+
+**Test Results:**
+```
+✅ Backend API exists (OpenAPI responding)
+✅ Frontend loads (HTML responding)
+❌ ALL API endpoints return 401 "Not authenticated"
+❌ Login endpoint rejects all credentials
+❌ Frontend shows inventory page without token
+```
+
+**Error Messages Explained:**
+- "Failed to process image with AI" → Frontend called `/items/` → 401 response  
+- "Failed to delete from database" → Frontend called `/items/{id}` → 401 response
+- "Failed to load admin data" → Frontend called `/admin/db/stats` → 401 response
+- "No + button to add item" → Item creation requires auth, frontend can't call API
+
+### Why User Saw Inventory Page (But No Data)
+
+**Expected Flow:**
+```
+1. User → http://localhost:8917/
+2. Frontend checks: localStorage.getItem('inventory_token')
+3. No token found
+4. Redirect to /login
+5. User logs in
+6. Token stored in localStorage
+7. Retry → inventory page loads with data
+```
+
+**Actual Flow:**
+```
+1. User → http://localhost:8917/
+2. Frontend shows inventory page ← SHOULD NOT HAPPEN (no token)
+3. Page tries to load data: getItems() → 401
+4. All API calls fail: create (401), delete (401), search (401)
+5. UI shows errors
+```
+
+**Root Cause:** Either:
+- Redirect to /login failed (race condition or bug in page.tsx)
+- OR token exists in localStorage but is invalid/malformed
+
+---
+
+## CODE PATHS VERIFIED
+
+### Frontend Authentication Setup ✅ CORRECT
+```typescript
+// frontend/lib/api.ts (lines 61-70)
+axios interceptor adds Bearer token to every request:
+- getToken() → reads from localStorage
+- config.headers.Authorization = `Bearer ${token}`
+- 401 handler redirects to /login
+```
+
+### Login Page ✅ EXISTS AND CORRECT
+```typescript
+// frontend/app/login/page.tsx
+- Loads users from backend
+- Accepts username/password
+- Calls inventoryApi.login()
+- Stores token using saveToken()
+- Redirects to /
+```
+
+### Auth Guard ✅ EXISTS
+```typescript
+// frontend/app/page.tsx (line 114-118)
+useEffect(() => {
+  if (!localStorage.getItem('inventory_token')) {
+    window.location.href = '/login';
+    return;
+  }
+  // ... load data
+}
+```
+
+### Backend Auth ✅ EXISTS
+```
+All endpoints protected with auth_guard decorator
+Default credentials: admin/admin (may not be initialized)
+Login endpoint: POST /users/login
+```
+
+---
+
+## THE FIX (Choose One)
+
+### Option A: Initialize Database with Test Credentials ⭐ RECOMMENDED
+```bash
+# Stop servers
+python3 start_servers.py stop
+
+# Run migration/init to create admin user
+# (or manually insert into database)
+
+# Start servers
+python3 start_servers.py start
+
+# Test: Login to http://localhost:8917/login with admin/admin
+```
+
+**Why:** Mirrors production setup, minimal code changes
+
+### Option B: Create Dev-Mode Auth Bypass (Quicker)
+Modify backend to allow unauthenticated access in development:
+```python
+# backend/main.py
+# Comment out or skip auth_guard for development
+# @app.get("/items/")
+# async def get_items(current_user = Depends(get_current_user)):
+# Change to:
+# @app.get("/items/")
+# async def get_items():  # No auth required
+```
+
+**Why:** Fastest fix, enables immediate testing
+
+### Option C: Fix Frontend Redirect Race Condition
+If token exists but redirect still happens:
+```typescript
+// frontend/app/page.tsx
+// Add logging to debug why redirect fires with valid token
+if (!localStorage.getItem('inventory_token')) {
+  console.log("No token found, redirecting to login");
+  window.location.href = '/login';
+}
+```
+
+**Why:** Addresses potential race condition
+
+---
+
+## WHAT WE KNOW WORKS
+
+✅ Backend API endpoints exist and are properly protected  
+✅ Frontend has correct auth handling  
+✅ Login page exists and calls backend correctly  
+✅ Axios interceptor adds tokens to all requests  
+✅ 401 handler redirects to login page  
+
+## WHAT'S BROKEN
+
+❌ No valid credentials exist in database (or admin user not initialized)  
+❌ User is seeing inventory page without authentication (redirect may have failed)  
+❌ All API calls return 401 because no valid token is being sent
+
+---
+
+## IMPLEMENTATION PLAN
+
+1. **Check Current State** (5 min)
+   - Verify if token exists in browser localStorage
+   - Check database for users table
+   - Attempt login with default credentials
+
+2. **Apply Fix** (10-30 min, depends on option chosen)
+   - Option A: Initialize admin user
+   - Option B: Add dev auth bypass
+   - Option C: Debug redirect issue
+
+3. **Verify Fix** (5 min)
+   - Run automated tests (phase6_with_auth.py)
+   - Verify all API endpoints respond with 200
+   - Test UI: create item, delete item, search, export
+
+4. **Complete Phase 6 Testing** (20 min)
+   - Manually test in browser
+   - Verify no console errors
+   - All functionality working
+
+---
+
+## SUCCESS CRITERIA
+
+✅ Login works (admin/admin or configured credentials)
+✅ Token is stored in localStorage  
+✅ All API endpoints return 200 (not 401)
+✅ Item creation works
+✅ Item deletion works
+✅ Search works
+✅ Export works
+✅ Admin panel loads
+
+---
+
+## AUTOMATED TESTS READY
+
+Run after fix is applied:
+```bash
+python3 tests/phase6_with_auth.py
+```
+
+Expected output: 7/7 tests passing
+
+---
+
+*Root Cause Analysis Complete*  
+*Ready for Phase 4: Implementation*  
+*Estimated fix time: 15-30 minutes*