FEATURE REQUEST: Replace default Flutter launcher icons with branded icons for Patient and Therapist apps

### Is your feature request related to a problem?

- [x] Yes, it is related to a problem

### Describe the feature you'd like

## Problem
Both the Patient and Therapist apps are still showing the default
Flutter launcher icon. This looks unfinished and doesn't reflect
the NeuroTrack brand at all.

## What I'm proposing
Add proper branded icons for both apps using the
`flutter_launcher_icons` package. I've already designed icons
matching each app's color scheme:
- Patient app → #7A86F8
- Therapist app → #CB6CE6

## Implementation
Add this configuration to `pubspec.yaml`:

flutter_launcher_icons:
android: true
ios: true

# iOS - full icon with background
image_path: "assets/icons/icon.png"

# Android - adaptive icon for Android 12+
adaptive_icon_foreground: "assets/icons/icon_foreground.png"
adaptive_icon_background: "assets/icons/icon_background.png"

# Web
web:
generate: true
image_path: "assets/icons/icon.png"
background_color: "#7A86F8"
theme_color: "#7A86F8"

# Windows
windows:
generate: true
image_path: "assets/icons/icon.png"
icon_size: 256

# macOS
macos:
generate: true
image_path: "assets/icons/icon.png"

remove_alpha_ios: true
min_sdk_android: 21

Then run:
dart run flutter_launcher_icons

## Icon Preview

Patient app icon     Therapist app icon

## I have the assets ready and happy to implement this if assigned.

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on implementing this feature