Move hardcoded configuration to environment variables

[Copilot]

Several configuration values were hardcoded in app_constants.dart and points.dart, requiring code changes to modify settings.

Changes

Configuration extraction:

• Notification settings (channel ID, name, description, icon)
• LED timing (on/off durations)
• Map distance threshold for proximity detection

Implementation:

• Added environment variable getters to AppConfig with fallback defaults
• Refactored AppConstants from static constants to getters delegating to AppConfig
• Updated .env.example with new variables and documentation
• Removed const modifiers in notification_service.dart where values are now runtime-evaluated

// Before
static const String notificationChannelId = 'high_importance_channel';
static const double _nearDistanceThreshold = 5000;

// After
static String get notificationChannelId => AppConfig.notificationChannelId;
double get _nearDistanceThreshold => AppConfig.nearDistanceThreshold;

All values maintain existing defaults when .env is absent. Commission rates were already environment-driven.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Hardcoded Configuration Values Instead of Environment Variables</issue_title>
<issue_description>

🟡 Medium Priority Issue

Problem

Some configuration values are hardcoded in the code instead of using environment variables, reducing flexibility.

Examples

• Default commission rates in app_config.dart:184,193
• Some Firebase configuration might be hardcoded
• Default values that should be configurable

Impact

• Less flexible configuration
• Requires code changes to modify settings
• Not following 12-factor app principles

Expected Behavior

All configurable values should be in environment variables with sensible defaults.

Solution

Move hardcoded values to environment variables:

1. Add to .env.example
2. Update app_config.dart to read from environment
3. Provide sensible defaults

Additional Context

The app already uses environment variables for most configuration, but some values are still hardcoded.

---</issue_description>

<agent_instructions>solve the isssue to make th dcode more bettter </agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Hardcoded Configuration Values Instead of Environment Variables #28

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