docs(README.md): update error handling section and improve API endpoint descriptions

docs(userscript/README.md): enhance configuration instructions and clarify connection testing
feat(userscript/simpleguardhome-404-checker.user.js): add connection testing and notification features for unblocking domains

userscript/README.md

@@ -6,7 +6,8 @@ A Tampermonkey userscript that detects 404 responses while browsing and automati
 
 - Automatically detects 404 responses from both fetch and XMLHttpRequest calls
 - Checks failed domains against your AdGuard Home instance
-- Shows notifications for blocked domains with unblock option
+- Shows notifications for blocked domains with one-click unblock button
+- Directly unblocks domains using SimpleGuardHome API
 - Configurable AdGuard Home instance settings
 - Caches results to minimize API calls
 - Error handling with configuration shortcuts
@@ -20,14 +21,28 @@ A Tampermonkey userscript that detects 404 responses while browsing and automati
 
 ## Configuration
 
+### Initial Setup
 1. Click on the Tampermonkey icon in your browser
-2. Select "Configure SimpleGuardHome Instance" under the script's menu
-3. Enter your AdGuard Home host (e.g., `http://localhost`)
-4. Enter your AdGuard Home port (default: 3000)
+2. Select "⚙️ Configure SimpleGuardHome" under the script's menu
+3. Review your current settings (if any)
+4. Enter new host and port settings
+5. Connection test will be performed automatically
+   - Success: Settings are saved immediately
+   - Failure: Option to save anyway or retry
+
+### Menu Options
+- "⚙️ Configure SimpleGuardHome" - Open configuration dialog
+- "🔄 Test Connection" - Test current settings
 
 ### Default Settings
 - Host: `http://localhost`
-- Port: `3000`
+- Port: `8000` (SimpleGuardHome default port)
+
+### Connection Testing
+- Automatic testing when saving new settings
+- Manual testing available through menu
+- Clear notifications of test results
+- Option to save settings even if test fails
 
 ## How It Works
 
@@ -35,8 +50,10 @@ A Tampermonkey userscript that detects 404 responses while browsing and automati
 2. When a 404 response is detected:
    - Extracts the domain from the failed URL
    - Checks if the domain is blocked by AdGuard Home
-   - Shows a notification if the domain is blocked
-   - Provides a quick "Unblock" button to open SimpleGuardHome
+   - Shows a notification with status if domain is blocked
+   - Provides a one-click "Unblock Domain" button
+   - Directly unblocks domain when button is clicked
+   - Shows success/error notification after unblock attempt
 
 3. Error handling:
    - Connection issues show a notification with configuration options
@@ -54,10 +71,11 @@ A Tampermonkey userscript that detects 404 responses while browsing and automati
 ### Cache System
 - Domain check results are cached for 1 hour
 - Cache includes:
-  - Block status
-  - Blocking reason
-  - Applied rules
+  - Block status (true/false)
   - Timestamp
+- Cache is updated when:
+  - Domain is checked (status: "not blocked", "blocked")
+  - Domain is unblocked (status: "already unblocked", "has been unblocked")
 
 ### Error Handling
 - Connection failures