fix(sync): restore UI state and task sync after reconnect or sleep (#107)

[Lexus2016]

Closes #107

Summary

Addresses session and task state divergence when closing the browser tab, computer sleeps/hibernates, or network disconnects.

Root Cause

1. In public/kanban.html, polling relied solely on setTimeout, which is paused by the browser when a tab is throttled or computer sleeps, with no visibilitychange, focus, or online events to trigger self-healing.
2. In public/index.html, when WebSocket reconnected while currentSessionId was already populated, loadSess was skipped. If a background task finished while away, the final response saved in the database was not loaded into the chat DOM.
3. In server.js, the 60s watchdog skipped any task present in taskRunning, even if its subprocess had already died (worker_pid no longer running), leaving stale tasks stuck in in_progress.

Changes

• public/kanban.html: Added visibilitychange, focus, and online event listeners to immediately refresh the board and restart auto-refresh upon wake-up.
• public/index.html: Added online event listener for immediate reconnection; updated reconnect and refocus handlers to call loadSess(activeTabId) so completed results, summaries, and checkmarks are rendered.
• server.js: Added isPidAlive(pid) helper and updated watchdog to evict dead worker_pid processes from taskRunning and recover stuck tasks.
• test/interrupted-recovery.test.js: Added test suite verifying watchdog isPidAlive checks, task recovery, and UI self-healing event bindings.