fix(security): add safeStorage fallback for production builds (#38)

* fix(security): add safeStorage fallback for production builds

- Replace hard keytar dependency with multi-strategy key storage:
  1. safeStorage (Electron built-in) - preferred
  2. keytar (system keychain) - fallback
  3. File-based encryption - last resort
- Dynamically import keytar to avoid hard failure in production
- Refactor cloudHandler to use const instead of let (Clean Code)
- Fix 'Failed to load cloud accounts' error in packaged app

The keytar native module fails to load from asar archives in
production builds. This fix ensures the app works even when
system keychain access is unavailable.

* refactor(security): address code review feedback

- Replace sync file ops with async (fs/promises)
- Add atomic file writes to prevent data races
- Implement concurrency lock for key generation
- Add SecurityError class with specific error codes:
  - KEY_STORAGE_FAILED, ENCRYPTION_FAILED, DECRYPTION_FAILED
  - INVALID_FORMAT, AUTH_TAG_MISMATCH, CORRUPTED_DATA
- Enhance error categorization in decrypt() for better diagnostics
- Add security warnings for file-based fallback mode

* fix: align error handling after merge

* feat: migrate legacy encrypted account data

* chore: enable beta prerelease workflow *skip release*

---------

Co-authored-by: Draculabo <[email protected]>

release.config.cjs

@@ -194,7 +194,7 @@ const appendReleaseNotesPlugin = {
 };
 
 const releaseConfig = {
-  branches: ['main', 'master'],
+  branches: ['main', { name: 'beta', prerelease: true }],
   plugins: [
     [
       '@semantic-release/commit-analyzer',