fix: improve error handling UI for Gaps and Try It screens

[jvsena42]

Summary

Fix error handling for the Gaps and Try It screens when the Claude API key is invalid or there is a request error. Previously, the Gaps screen showed a loading spinner forever on API failure, and both screens displayed raw/technical error messages (e.g., JSON parse errors). Now, ClaudeApiClient checks HTTP status codes and returns user-friendly messages, the Gaps screen displays a proper error state with retry, and the Try It screen's inline error was upgraded to a styled error content with retry button.

Changes

• Add HTTP status code checking in ClaudeApiClient.sendRequest() — maps 401, 429, 5xx to user-friendly error messages and catches network exceptions
• Add ClaudeErrorResponse / ClaudeErrorDetail models to ClaudeApiModels.kt
• Add ErrorContent composable to Android GapsScreen with error icon, message, and retry button
• Add errorContent(message:) view to iOS GapsScreen.swift with matching design
• Replace simple ErrorMessage with styled ErrorContent (icon + message + retry) on Android TryItScreen
• Replace simple errorMessage() with styled errorContent(message:) on iOS TryItScreen.swift
• Add common_retry string resource to all 4 locale files (en/pt-BR for Android and iOS)

Test plan

• Set an invalid API key in Settings, navigate to Gaps screen → should show error with "Invalid API key" message and Retry button
• Tap Retry → should reload and show the same error (or succeed if key was corrected)
• Set an invalid API key, navigate to Try It screen, take a photo, tap Analyze → should show styled error content with Retry button
• Tap Retry → should re-attempt analysis
• Verify both screens on Android and iOS

Checklist

• ./gradlew detekt passes
• Tested on Android
• Tested on iOS
• Updated documentation (if applicable)