refactor: rimuove cache destinazione e forza rescansione completa

- elimina cache su disco in destination scanner
- rimuove integrazione cache da main process
- allinea messaggi progresso UI alla scansione completa
- aggiorna README con comportamento senza cache

main.js

@@ -4,7 +4,6 @@ const fs = require('fs-extra');
 
 const { processFolder } = require('./services/folderProcessor');
 const { processZip } = require('./services/zipProcessor');
-const { setCacheDir, clearCache } = require('./services/destinationScanner');
 const {
   resolveUnroutedDir,
   listUnroutedFiles,
@@ -128,7 +127,6 @@ Menu.setApplicationMenu(Menu.buildFromTemplate([
 
 app.whenReady().then(async () => {
   await ensureRuntimeDirectory();
-  setCacheDir(getRuntimeDirectory());
   const persistedDestination = await loadPersistedDestination();
   config = buildConfig(persistedDestination);
   createWindow();
@@ -226,7 +224,6 @@ ipcMain.handle('update-destination', async (_event, payload) => {
 
   config = buildConfig(destination);
   await persistDestination(config.destination);
-  await clearCache();
   return { destination: config.destination };
 });