Add 10 UX/feature improvements across dashboard, status page, and API

- Incident acknowledge: Ack button in dashboard rail and ResourceDetail incidents table
- Status page 90-day uptime history bars (teal ≥99%, amber ≥95%, red <95%, grey = no data)
- Theme setting applied: data-theme attribute wired to saved setting with CSS variables + light mode overrides
- Sparkline replaced with colored status bars (teal=up, red=down, grey=unknown) per check tick
- ResourceDetail chart time-range selector: 1h / 6h / 24h / 7d toggle fetches from checks endpoint
- Bulk actions: checkbox per row, select-all header, bulk delete and maintenance toggle bar
- CSV export adds 6 new fields (http_method, http_body, heartbeat_timeout, is_public, consecutive_failures_threshold, response_time_threshold)
- CSV import handles those 6 new fields on INSERT
- Check detail expansion: click expandable rows in Recent Checks to show full details JSON
- Browser push notifications: request permission opt-in, new Notification() on WS message when tab unfocused

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

client/build/index.html

@@ -1 +1 @@
-<!doctype html><html lang="en"><head><meta charset="utf-8"/><link rel="icon" type="image/png" href="/app-icon.png"/><meta name="viewport" content="width=device-width,initial-scale=1"/><meta name="theme-color" content="#000000"/><meta name="description" content="SkyWatch - Infrastructure monitoring and alerting system"/><link rel="apple-touch-icon" href="/app-icon.png"/><link rel="manifest" href="/manifest.json"/><title>SkyWatch</title><script defer="defer" src="/static/js/main.a387bcf0.js"></script><link href="/static/css/main.5afb44a9.css" rel="stylesheet"></head><body><noscript>You need to enable JavaScript to run this app.</noscript><div id="root"></div></body></html>
+<!doctype html><html lang="en"><head><meta charset="utf-8"/><link rel="icon" type="image/png" href="/app-icon.png"/><meta name="viewport" content="width=device-width,initial-scale=1"/><meta name="theme-color" content="#000000"/><meta name="description" content="SkyWatch - Infrastructure monitoring and alerting system"/><link rel="apple-touch-icon" href="/app-icon.png"/><link rel="manifest" href="/manifest.json"/><title>SkyWatch</title><script defer="defer" src="/static/js/main.85e69234.js"></script><link href="/static/css/main.67d2dbc4.css" rel="stylesheet"></head><body><noscript>You need to enable JavaScript to run this app.</noscript><div id="root"></div></body></html>