Adds a white-label configurable arrival/departure filter

[diveshpatil9104]

Summary

Adds a white-label configurable arrival/departure filter that lets users choose which departures to display: All, Real-Time Only, or Scheduled Only. Closes #597.

Problem: Transit agencies using the white-label framework wanted to control whether scheduled (non-real-time) arrivals are shown. Some agencies have unreliable schedule data, and displaying "arrives 5 min late" highlights poor service performance. They needed the ability to hide scheduled arrivals when real-time data is unavailable.

Solution: A global ArrivalDepartureFilter setting accessible from both the Settings page and a Departure Type menu on each stop view. Brands can configure the default via CoreAppConfig.defaultArrivalDepartureFilter.

Changes

• StopPreferences.swift — Added ArrivalDepartureFilter enum (.all, .estimatedOnly, .scheduledOnly)
• CoreAppConfig.swift — Added defaultArrivalDepartureFilter property for white-label brand default + shared UserDefaults key
• AppConfig.swift — Pass-through for new config parameter
• ArrivalDeparture.swift — Added filter(by:) extension on [ArrivalDeparture] using the predicted property
• StopViewController.swift — Reads global filter from UserDefaults, applies to both time-sorted and route-sorted views, adds Departure Type submenu
• SettingsViewController.swift — Added Arrival Display section with AlertRow for global filter preference
• ArrivalDepartureFilterTests.swift — Unit tests for filter logic, enum, empty arrays, complementary counts, and UserDefaults round-trips

Screenshots / Demo

Implementation.mp4

Test Plan

• Unit tests pass (ArrivalDepartureFilterTests, ArrivalDepartureFilterEnumTests, ArrivalDepartureFilterUserDefaultsTests)
• Open a stop with mixed real-time and scheduled arrivals
• Tap ⋯ menu → Departure Type → Real-Time Only — verify only real-time arrivals remain
• Tap Departure Type → Scheduled Only — verify only scheduled arrivals remain
• Tap Departure Type → All Departures — verify all arrivals return
• Navigate to a different stop — verify same filter applies (global setting)
• Open Settings → Arrival Display → Show Departures — verify AlertRow shows current selection
• Change filter in Settings, go back to a stop — verify filter is applied
• Switch sort mode (time vs route) — verify filter works in both modes
• Kill and relaunch app — verify filter preference persists