fix: retroachievements setup now works on Linux without a keyring (#126)

Previously failed with a confusing "check your credentials" error when
the system keyring wasn't available. Now falls back to plaintext storage.

---
Uses a `plain:` prefix to distinguish unencrypted keys from encrypted
ones, so existing encrypted keys keep working.

Fixes #125

Author: JZimz

src/main/db/queries/integrations.ts

@@ -7,23 +7,28 @@ const log = logger.scope('db:integrations');
 
 const RA_USERNAME_KEY = 'integration.retroachievements.username';
 const RA_API_KEY = 'integration.retroachievements.apiKey';
+const PLAINTEXT_PREFIX = 'plain:';
 
 export const integrationsQueries = {
   getRetroAchievements(): RetroAchievementsConfig | null {
     const username = settingsQueries.get(RA_USERNAME_KEY);
-    const encryptedApiKey = settingsQueries.get(RA_API_KEY);
+    const storedApiKey = settingsQueries.get(RA_API_KEY);
 
-    if (!username || !encryptedApiKey) {
+    if (!username || !storedApiKey) {
       return null;
     }
 
+    if (storedApiKey.startsWith(PLAINTEXT_PREFIX)) {
+      return { username, apiKey: storedApiKey.slice(PLAINTEXT_PREFIX.length) };
+    }
+
     if (!safeStorage.isEncryptionAvailable()) {
-      log.warn('Encryption not available on this system, cannot decrypt RetroAchievements API key');
+      log.warn('Encryption not available and no plaintext fallback found');
       return null;
     }
 
     try {
-      const encryptedBuffer = Buffer.from(encryptedApiKey, 'base64');
+      const encryptedBuffer = Buffer.from(storedApiKey, 'base64');
       const apiKey = safeStorage.decryptString(encryptedBuffer);
       return { username, apiKey };
     } catch (error) {
@@ -35,16 +40,19 @@ export const integrationsQueries = {
   setRetroAchievements(config: RetroAchievementsConfig) {
     const { username, apiKey } = config;
 
-    if (!safeStorage.isEncryptionAvailable()) {
-      throw new Error('Encryption not available on this system, cannot store API key securely');
+    if (safeStorage.isEncryptionAvailable()) {
+      const encryptedApiKey = safeStorage.encryptString(apiKey);
+      settingsQueries.setMany({
+        [RA_USERNAME_KEY]: username,
+        [RA_API_KEY]: encryptedApiKey.toString('base64'),
+      });
+    } else {
+      log.warn('Secure storage unavailable, storing API key in plaintext');
+      settingsQueries.setMany({
+        [RA_USERNAME_KEY]: username,
+        [RA_API_KEY]: PLAINTEXT_PREFIX + apiKey,
+      });
     }
-
-    const encryptedApiKey = safeStorage.encryptString(apiKey);
-
-    settingsQueries.setMany({
-      [RA_USERNAME_KEY]: username,
-      [RA_API_KEY]: encryptedApiKey.toString('base64'),
-    });
   },
 
   removeRetroAchievements() {