refactor(semantics): migrate legacy @TIER to @COMPLEXITY annotations

- Replaced @TIER: TRIVIAL with @COMPLEXITY: 1
- Replaced @TIER: STANDARD with @COMPLEXITY: 3
- Replaced @TIER: CRITICAL with @COMPLEXITY: 5
- Manually elevated specific critical/complex components to levels 2 and 4
- Ignored legacy, specs, and node_modules directories
- Updated generated semantic map

frontend/src/lib/i18n/index.ts

@@ -1,6 +1,6 @@
 // [DEF:i18n:Module]
 //
-// @TIER:      STANDARD
+// @COMPLEXITY: 3
 // @SEMANTICS: i18n, localization, svelte-store, translation
 // @PURPOSE:   Centralized internationalization management using Svelte stores.
 // @LAYER:     Infra