feat(i18n): add Phase 3 observability translations (EN + PL)

Added translations for all observability components:
- Validation warnings panel
- Auto-fixes badge
- AI reasoning process viewer
- Debug information panel
- Structured error display

English translations (en.json):
- observability_validationWarnings: "Validation Warnings"
- observability_autoFixesApplied: "Automatically adjusted"
- observability_aiReasoningProcess: "AI Reasoning Process"
- observability_debugInfo: "Debug Information"
- observability_model/duration/tokenUsage: Debug panel labels
- observability_validationFailed: "Safety validation failed"

Polish translations (pl.json):
- observability_validationWarnings: "Ostrzeżenia walidacji"
- observability_autoFixesApplied: "Automatycznie dostosowano"
- observability_aiReasoningProcess: "Proces rozumowania AI"
- observability_debugInfo: "Informacje debugowania"
- All debug panel labels translated
- observability_validationFailed: "Walidacja bezpieczeństwa nie powiodła się"

Updated components:
- ValidationWarningsAlert: Uses m.observability_validationWarnings()
- AutoFixBadge: Uses m.observability_autoFixesApplied()
- ReasoningChainViewer: Uses m.observability_aiReasoningProcess()
- MetadataDebugPanel: All labels now use i18n
- StructuredErrorDisplay: Translates error prefixes

All components now fully support English and Polish locales.

frontend/src/lib/components/StructuredErrorDisplay.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { XCircle } from 'lucide-svelte';
+	import { m } from '$lib/paraglide/messages.js';
 
 	interface Props {
 		error: string;
@@ -25,6 +26,20 @@
 	const cleanedErrors = $derived(
 		hasPrefix && prefix ? [errors[0].substring(prefix.length)] : errors
 	);
+
+	// Translate known error prefixes
+	const translatedPrefix = $derived(() => {
+		if (!prefix) return '';
+		const prefixText = prefix.replace(':', '').trim();
+		// Check for common validation failure prefix
+		if (
+			prefixText.includes('safety validation') ||
+			prefixText.includes('validation')
+		) {
+			return m.observability_validationFailed();
+		}
+		return prefixText;
+	});
 </script>
 
 <div class="editorial-alert editorial-alert--error">
@@ -32,7 +47,7 @@
 		<XCircle class="size-5 shrink-0 mt-0.5" />
 		<div class="flex-1">
 			{#if prefix}
-				<p class="font-medium mb-2">{prefix.replace(':', '')}</p>
+				<p class="font-medium mb-2">{translatedPrefix()}</p>
 			{/if}
 			{#if cleanedErrors.length === 1}
 				<p>{cleanedErrors[0]}</p>