iOS 26 modernization — @Observable state, async networking, Liquid Glass UI, notifications

[bsakhuja]

Summary

• Fix filter live-update bug — all SettingsState filter properties were @ObservationIgnored @AppStorage, making @Observable blind to changes; replaced with plain stored properties + didSet UserDefaults persistence so filters, chip labels, and the list update instantly without restarting
• Fix map/list toggle reliability — moved isListView from @ObservationIgnored @AppStorage in SettingsState to direct @AppStorage on HomeView so SwiftUI tracks it natively
• @observable migration — all three state classes migrated from ObservableObject/@StateObject/@EnvironmentObject to @Observable/@State/@Environment
• Async network layer — replaced Combine AnyPublisher with async/await; added 2-retry exponential backoff, removed bogus Authorization: Bearer TOKEN header, configured URLCache; errors surface via alert with retry button
• Liquid Glass UI — glassEffect() on cards, .toolbarBackground(.glass), 5-tier magnitude color system (Color+Magnitude.swift)
• Earthquake notifications — new NotificationManager with BGAppRefreshTask for background M5.0+ alerts with deduplication; registered in RumbleApp
• Inline filter chips — date, magnitude, and sort controls moved into a horizontal scroll row at the top of the list; settings screen simplified to notifications only
• Segmented nav control — map/list toggle replaced with Picker(.segmented) in .principal toolbar slot; .navigationBarTitleDisplayMode(.inline) prevents the "Earthquakes" title from floating over the map
• Map location button — moved from mapControls to a custom .regularMaterial circle button overlaid .bottomTrailing, with MapCameraPosition binding so tapping it re-centers on the user

Test plan

• Changing a filter chip (date range, magnitude, sort) updates the list immediately without restarting
• Map/list segmented control switches views with crossfade; selection persists across restarts
• Pulling to refresh re-fetches and shows an error alert (with Retry) if the network is offline
• Tapping the location button on the map re-centers on user location
• Notifications section in Settings toggles correctly; minimum magnitude picker appears when enabled
• All magnitude colors render correctly (green → yellow → orange → red → dark red)
• App builds cleanly in Release with no errors

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