Fix high CPU usage from notifications and add regression tests

- Fix auto-updating Text(date, style: .time) causing continuous SwiftUI updates
  by using static formatting with .formatted(date:time:)
- Fix notification popover keeping SwiftUI observers active when closed by
  clearing contentViewController on popover close and recreating on open
- Fix focus loss when notifications arrive while typing by only setting
  focus in NotificationsPage when the page is visible
- Make Update Pill and Update Logs debug-only features
- Add CPU regression tests: test_cpu_usage.py, test_cpu_notifications.py
- Add lint test for auto-updating Text patterns: test_lint_swiftui_patterns.py

Sources/Update/UpdateLogStore.swift

@@ -20,6 +20,7 @@ final class UpdateLogStore {
     }
 
     func append(_ message: String) {
+        #if DEBUG
         let timestamp = formatter.string(from: Date())
         let line = "[\(timestamp)] \(message)"
         queue.async { [weak self] in
@@ -30,6 +31,7 @@ final class UpdateLogStore {
             }
             appendToFile(line: line)
         }
+        #endif
     }
 
     func snapshot() -> String {