Implement improved version handling and semantic versioning

- Add semver library for semantic version comparison
- Make package.json the single source of truth for version
- Add version check to only offer updates when remote version is higher
- Use APP_VERSION constant throughout server instead of hardcoded values
- Refactor update checking logic to use semver.gt() for proper comparison

This change improves robustness by ensuring updates are only
offered when a higher semantic version is available in the repository.

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

server.js

@@ -25,6 +25,10 @@ const DEFAULT_PORT = 3000;
 const JWT_SECRET = process.env.JWT_SECRET || 'transmission-rss-manager-secret';
 const JWT_EXPIRY = '24h';
 
+// Get the version from package.json (single source of truth)
+const PACKAGE_JSON = require('./package.json');
+const APP_VERSION = PACKAGE_JSON.version;
+
 // Create Express app
 const app = express();
 
@@ -92,7 +96,7 @@ async function loadConfig() {
   try {
     // Define default configuration
     const defaultConfig = {
-      version: '2.0.0',
+      version: APP_VERSION, // Use the version from package.json
       transmissionConfig: {
         host: 'localhost',
         port: 9091,
@@ -152,9 +156,9 @@ async function loadConfig() {
       const mergedConfig = mergeConfigs(defaultConfig, loadedConfig);
       
       // If version is different, save updated config
-      if (loadedConfig.version !== defaultConfig.version) {
-        console.log(`Updating config from version ${loadedConfig.version || 'unknown'} to ${defaultConfig.version}`);
-        mergedConfig.version = defaultConfig.version;
+      if (loadedConfig.version !== APP_VERSION) {
+        console.log(`Updating config from version ${loadedConfig.version || 'unknown'} to ${APP_VERSION}`);
+        mergedConfig.version = APP_VERSION;
         await saveConfig(mergedConfig);
       }