i18n: backend-localized lookups, suggestions, and static data (10 languages)

- suggestion_service: fix scorer (stringList unmarshal accepts scalar|array;
  anchor scoring on base universal score so bool matches no longer tie); add
  localizeReasons for human-readable, Accept-Language-localized match reasons
- lookup_i18n: localize lookup display names, home-profile options, document
  types/categories via internal/i18n
- static_data_handler: per-locale seeded-data response (display_name, home
  profile options, document types/categories) with per-locale cache + ETag
- settings_handler: invalidate per-locale seeded-data cache on lookup change
  instead of pre-warming a single non-localized blob
- cache_service: per-locale seeded-data keys + ETag
- DTOs: add DisplayName fields (task/residence/contractor)
- translations: add suggestion.reason.* and lookup.* keys across all 10 langs
- cmd/api: extract startup helpers + tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/dto/responses/contractor.go

@@ -8,8 +8,11 @@ import (
 
 // ContractorSpecialtyResponse represents a contractor specialty
 type ContractorSpecialtyResponse struct {
-	ID           uint   `json:"id"`
-	Name         string `json:"name"`
+	ID uint `json:"id"`
+	// Name is the stable English identifier (clients match on this).
+	Name string `json:"name"`
+	// DisplayName is the localized label for the request's Accept-Language.
+	DisplayName  string `json:"display_name"`
 	Description  string `json:"description"`
 	Icon         string `json:"icon"`
 	DisplayOrder int    `json:"display_order"`