Fix backend API parity: document filters, task days param, i18n locales, contract tests

- Add document list filter support (residence, type, category, contractor, is_active, expiring_soon, search) to handler/service/repo
- Add `days` query param parsing to ListTasks handler (matches ListTasksByResidence)
- Add `error.invalid_token` i18n key to all 9 non-English locale files
- Update contract test to include VerificationResponse mapping

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/integration/kmp_model_contract_test.go

@@ -262,7 +262,7 @@ var excludedSchemas = map[string]string{
 	"SharePackageResponse":              "Used for .casera file sharing, handled by SharedContractor",
 	"UnregisterDeviceRequest":           "Simple oneoff request",
 	"UpdateTaskCompletionRequest":       "Not yet used in KMP",
-	"SubscriptionResponse":              "Different shape — SubscriptionStatusResponse is mapped",
+	"SubscriptionResponse":              "Inline in purchase/restore handler — KMP maps via VerificationResponse.subscription",
 	"UpgradeTriggerResponse":            "Shape differs from KMP UpgradeTriggerData",
 	"UploadResult":                      "Handled inline in upload response parsing",
 }