fix(packaging): workaround yauzl/Node 26 hang + fix API bootstrap contract

Packaging was silently hanging forever because yauzl 2.10.0 read streams
emit no data events under Node 26, causing extract-zip to block indefinitely
inside @electron/packager 20. Fix: postinstall script patches
@electron/packager/dist/unzip.js to use bsdtar (libarchive) instead.
bsdtar was chosen over 7z because 7z refuses chained symlinks in macOS
.app framework bundles. Both package:linux and package:mac now produce
correct output.

Also corrects the V3 API bootstrap contract in api_client.ts:
- SearchQuery body was wrapped in an extra {search_query: ...} layer — removed
- x-no-account-id header standardised to 'bypass'
- Redundant x-no-account-id removed from file download headers
- Smoke test rewritten to validate the real two-step bootstrap path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/file_handlers.ts

@@ -67,8 +67,7 @@ export function registerFileHandlers() {
         method: 'get', url, responseType: 'stream',
         headers: {
           'x-aether-api-key': api_key,
-          'x-account-id': account_id || '',
-          'x-no-account-id': 'Nothing to See Here'
+          'x-account-id': account_id || ''
         }
       });