Recover Electron renderer after blank-page crashes

[danshapiro]

Summary:

• add durable Electron main-process JSONL logging with redaction
• supervise the main renderer for crash, load-failure, and unresponsive blank-page recovery
• replace unusable crashed BrowserWindows during recovery while preserving external-link IPC
• add focused unit coverage and Electron e2e crash recovery coverage

Verification:

• FRESHELL_TEST_SUMMARY="rebased electron renderer recovery before PR" npm run check
• client: 358 files, 3,878 tests passed
• server: 273 passed / 1 skipped files, 4,142 passed / 9 skipped tests
• electron: 33 files, 347 tests passed