Fix update functionality and improve documentation

- Fixed update detection in install scripts
- Added Git availability checks to update system
- Improved error handling for update endpoint
- Added detailed Git requirements to README
- Added troubleshooting section for update issues

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

main-installer.sh

@@ -28,6 +28,10 @@ source "${SCRIPT_DIR}/modules/utils-module.sh"
 echo -e "${BOLD}==================================================${NC}"
 echo -e "${BOLD}     Transmission RSS Manager Installer           ${NC}"
 VERSION=$(grep -oP '"version": "\K[^"]+' "${SCRIPT_DIR}/package.json" 2>/dev/null || echo "Unknown")
+# Check if package.json exists, if not suggest creating it
+if [ ! -f "${SCRIPT_DIR}/package.json" ]; then
+  echo -e "${YELLOW}Warning: package.json not found. You may need to run 'npm init' first.${NC}"
+fi
 echo -e "${BOLD}     Version ${VERSION} - Git Edition                  ${NC}"
 echo -e "${BOLD}==================================================${NC}"
 echo
@@ -42,35 +46,74 @@ fi
 IS_UPDATE=false
 INSTALLATION_DETECTED=false
 
-# Check for config.json file (primary indicator)
-if [ -f "${SCRIPT_DIR}/config.json" ]; then
-  INSTALLATION_DETECTED=true
-fi
-
-# Check for service file (secondary indicator)
-if [ -f "/etc/systemd/system/transmission-rss-manager.service" ]; then
+# Check if we have existing config info from install-script.sh
+if [ -n "$EXISTING_INSTALL_DIR" ] && [ -n "$EXISTING_CONFIG_PATH" ]; then
   INSTALLATION_DETECTED=true
+  IS_UPDATE=true
+  # Use the existing installation directory as our target
+  INSTALL_DIR="$EXISTING_INSTALL_DIR"
+  CONFIG_FILE="$EXISTING_CONFIG_PATH"
+  log "INFO" "Using existing installation at $INSTALL_DIR detected by install-script.sh"
+  export INSTALL_DIR
+else
+  # Check for config.json file (primary indicator)
+  POSSIBLE_CONFIG_LOCATIONS=(
+    "${SCRIPT_DIR}/config.json"
+    "/opt/transmission-rss-manager/config.json"
+    "/etc/transmission-rss-manager/config.json"
+  )
   
-  # Check if the service points to /opt/trans-install
-  if grep -q "/opt/trans-install" "/etc/systemd/system/transmission-rss-manager.service"; then
-    # Set INSTALL_DIR to match existing service file
-    INSTALL_DIR="/opt/trans-install"
-    log "INFO" "Found existing installation at /opt/trans-install - using this as installation directory"
-    export INSTALL_DIR
+  for CONFIG_PATH in "${POSSIBLE_CONFIG_LOCATIONS[@]}"; do
+    if [ -f "$CONFIG_PATH" ]; then
+      INSTALLATION_DETECTED=true
+      IS_UPDATE=true
+      INSTALL_DIR="$(dirname "$CONFIG_PATH")"
+      CONFIG_FILE="$CONFIG_PATH"
+      log "INFO" "Found existing installation at $INSTALL_DIR"
+      export INSTALL_DIR
+      break
+    fi
+  done
+  
+  # Check for service file (secondary indicator) if no config file found
+  if [ "$INSTALLATION_DETECTED" = "false" ] && [ -f "/etc/systemd/system/transmission-rss-manager.service" ]; then
+    INSTALLATION_DETECTED=true
+    IS_UPDATE=true
+    
+    # Extract the installation directory from the service file
+    SERVICE_INSTALL_DIR=$(grep "WorkingDirectory=" "/etc/systemd/system/transmission-rss-manager.service" | cut -d'=' -f2)
+    if [ -n "$SERVICE_INSTALL_DIR" ]; then
+      INSTALL_DIR="$SERVICE_INSTALL_DIR"
+      log "INFO" "Found existing installation at $INSTALL_DIR from service file"
+      export INSTALL_DIR
+      
+      # Check for config file in the detected installation directory
+      if [ -f "$INSTALL_DIR/config.json" ]; then
+        CONFIG_FILE="$INSTALL_DIR/config.json"
+      fi
+    fi
+  fi
+  
+  # Check for data directory (tertiary indicator)
+  if [ "$INSTALLATION_DETECTED" = "false" ] && [ -d "${SCRIPT_DIR}/data" ] && [ "$(ls -A "${SCRIPT_DIR}/data" 2>/dev/null)" ]; then
+    INSTALLATION_DETECTED=true
   fi
 fi
 
-# Check for data directory (tertiary indicator)
-if [ -d "${SCRIPT_DIR}/data" ] && [ "$(ls -A "${SCRIPT_DIR}/data" 2>/dev/null)" ]; then
-  INSTALLATION_DETECTED=true
-fi
-
-if [ "$INSTALLATION_DETECTED" = true ]; then
-  IS_UPDATE=true
+# Provide clear feedback about the installation type
+if [ "$IS_UPDATE" = "true" ]; then
+  log "INFO" "Running in UPDATE mode - will preserve existing configuration"
+  log "INFO" "Target installation directory: $INSTALL_DIR"
+  if [ -n "$CONFIG_FILE" ]; then
+    log "INFO" "Using configuration file: $CONFIG_FILE"
+  fi
+  
+  # Make sure the variables are set correctly
   echo -e "${YELLOW}Existing installation detected. Running in update mode.${NC}"
   echo -e "${GREEN}Your existing configuration will be preserved.${NC}"
   echo -e "${GREEN}Only application files will be updated.${NC}"
 else
+  log "INFO" "Running in FRESH INSTALL mode"
   echo -e "${GREEN}Fresh installation. Will create new configuration.${NC}"
 fi
 export IS_UPDATE