TP-14 — Add LRU cache for parsed themes

[ZhuchkaTriplesix]

Epic: B
Depends on: TP-13

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

Goal

Avoid repeated file reads and parsing when switching between themes.

Files

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

Implementation

Inside ThemeRegistryService:

• cache QueryaTheme by definition.stableCacheKey;
• max entries: 12 or 20;
• on cache hit, return cached theme;
• on content hash change, key changes naturally;
• expose clearCache() for tests/reset.

If current project has no LRU helper, implement tiny private LRU using LinkedHashMap.

Acceptance Criteria

• Loading same definition twice parses once.
• Loading changed file parses again.
• Cache evicts oldest entry after limit.

Tests

• fake parser counter or temp file mutation;
• cache hit;
• cache invalidation by hash;
• eviction.

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