TP-13 — Load selected theme by definition

[ZhuchkaTriplesix]

Epic: B
Depends on: TP-12, TP-09

Source: docs/theme-parser-github-issues.md

Goal

Given a ThemeDefinition, parse the full theme and return ThemeLoadResult.

Files

• lib/core/theme/theme_registry_service.dart
• test/core/theme/theme_registry_service_test.dart

Implementation

Add:

Future<ThemeLoadResult> loadTheme(ThemeDefinition definition)

Behavior:

• ThemeFormat.queryaCustom -> QueryaThemeManifest.fromJsonString -> queryaThemeFromManifest.
• ThemeFormat.vscode -> existing VsCodeThemeManifest -> existing queryaThemeFromVsCode.
• failure -> ThemeLoadFailure.
• missing file -> ThemeLoadFailure.

Acceptance Criteria

• Custom definition loads to QueryaTheme.
• VS Code definition still loads.
• Missing/deleted file returns failure.
• No app crash on parse failure.

Tests

• custom success;
• VS Code success using existing fixture;
• deleted file failure;
• invalid file failure.

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