Fix iOS widget date formatting for RFC3339 dates

- Add centralized formatWidgetDate() helper that handles both yyyy-MM-dd and ISO8601 formats
- Update widget date display to show "Today", "in X days", or "X days ago"
- Fix isTaskOverdue() to parse ISO8601 dates from Go API
- Remove duplicate date formatting functions from widget views
- Switch API environment back to DEV

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/com/example/casera/network/ApiConfig.kt

@@ -9,7 +9,7 @@ package com.example.casera.network
  */
 object ApiConfig {
     // ⚠️ CHANGE THIS TO TOGGLE ENVIRONMENT ⚠️
-    val CURRENT_ENV = Environment.LOCAL
+    val CURRENT_ENV = Environment.DEV
 
     enum class Environment {
         LOCAL,