TP-11 — Add theme paths helper

[ZhuchkaTriplesix]

Epic: B
Depends on: TP-10

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

Goal

Centralize app theme directories and avoid path logic scattered across services.

Files

• lib/core/theme/theme_paths.dart
• test/core/theme/theme_paths_test.dart if path provider can be faked easily.

Implementation

Add:

abstract final class ThemePaths {
  static Future<Directory> userThemesDirectory();
  static Future<Directory> importedThemesDirectory();
}

Rules:

• Primary user dir: app support directory + themes.
• Imported dir: app support directory + themes/imported.
• Optionally expose legacyDotQueryaThemesDirectory() for later ~/.querya/themes.

Acceptance Criteria

• Directories are not created by path getter unless method name says ensure.
• Separate ensureUserThemesDirectory() can create it.

Tests

• If existing test support fakes path provider, assert paths.
• Otherwise cover through registry tests.

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