Visual fixes + schedule sticky headers

[jfversluis]

No description provided.

[Copilot]

Pull Request Overview

This PR implements visual improvements and adds sticky header functionality to the conference app's schedule feature. The changes focus on improving UI consistency, error handling, and user experience through better visual feedback and smooth header transitions.

• Replaces toast notifications with in-line error messages for better UX
• Adds sticky header behavior to schedule pages with smooth animations
• Optimizes UI layouts for better performance and visual consistency

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
SpeakersViewModel.cs	Improved error handling with timeout and better fallback logic
ScheduleViewModel.cs	Similar error handling improvements to SpeakersViewModel
RefreshService.cs	Simplified using statement for ToastDuration
Styles.xaml	Reduced margins and adjusted visual styling for consistency
SpeakersPage.xaml.cs	Simplified constructor and removed manual refresh handling
SpeakersPage.xaml	Complete UI redesign with loading states and error handling
SchedulePage.xaml.cs	Added sticky header support and simplified refresh handling
SchedulePage.xaml	Integrated sticky header behavior and improved layout
MauiProgram.cs	Added Controls namespace import
StickyHeaderBehavior.cs	New custom behavior for sticky headers with animations

Comments suppressed due to low confidence (2)

src/Conference.Maui/ViewModels/SpeakersViewModel.cs:130

• The early return guard for IsRefreshing was removed, which could lead to multiple concurrent refresh operations if the user triggers refresh multiple times quickly. This can cause race conditions and duplicate data loading.

        try

src/Conference.Maui/ViewModels/ScheduleViewModel.cs:168

• The early return guard for IsRefreshing was removed, which could lead to multiple concurrent refresh operations if the user triggers refresh multiple times quickly. This can cause race conditions and duplicate data loading.

        try