feat: add evaluation persistence layer

Add EvaluationPersistence class for localStorage state management.
Enables resume capability for long-running evaluations (5-15 min) after page reload.
Includes staleness check (1 hour).

Author: bekmuradov

src/evaluation-view/EvaluationPersistence.ts

@@ -0,0 +1,93 @@
+import type { ModelInfo, PersonaInfo } from '../components/chat-header/types';
+import type { TestCase, SubmissionItem } from './evaluationViewTypes';
+
+const STORAGE_KEY = 'braindrive_evaluation_in_progress';
+const MAX_AGE_MS = 60 * 60 * 1000; // 1 hour
+
+export interface PersistedEvaluationState {
+  runId: string;
+  model: ModelInfo;
+  persona: PersonaInfo | null;
+  collectionId?: string;
+  testCases: TestCase[];
+  processedQuestionIds: string[];
+  currentBatch: SubmissionItem[];
+  timestamp: number;
+}
+
+export class EvaluationPersistence {
+  /**
+   * Save evaluation state to localStorage
+   */
+  static saveState(state: PersistedEvaluationState): void {
+    try {
+      const stateWithTimestamp = {
+        ...state,
+        timestamp: Date.now(),
+      };
+      localStorage.setItem(STORAGE_KEY, JSON.stringify(stateWithTimestamp));
+    } catch (error) {
+      console.error('Failed to save evaluation state:', error);
+    }
+  }
+
+  /**
+   * Load evaluation state from localStorage
+   */
+  static loadState(): PersistedEvaluationState | null {
+    try {
+      const stored = localStorage.getItem(STORAGE_KEY);
+      if (!stored) return null;
+
+      const state = JSON.parse(stored) as PersistedEvaluationState;
+
+      // Check if state is stale
+      if (this.isStale(state)) {
+        this.clearState();
+        return null;
+      }
+
+      return state;
+    } catch (error) {
+      console.error('Failed to load evaluation state:', error);
+      return null;
+    }
+  }
+
+  /**
+   * Clear evaluation state from localStorage
+   */
+  static clearState(): void {
+    try {
+      localStorage.removeItem(STORAGE_KEY);
+    } catch (error) {
+      console.error('Failed to clear evaluation state:', error);
+    }
+  }
+
+  /**
+   * Check if state is stale (older than 1 hour)
+   */
+  static isStale(state: PersistedEvaluationState): boolean {
+    const age = Date.now() - state.timestamp;
+    return age > MAX_AGE_MS;
+  }
+
+  /**
+   * Check if there's an in-progress evaluation
+   */
+  static hasInProgressEvaluation(): boolean {
+    const state = this.loadState();
+    return state !== null;
+  }
+
+  /**
+   * Get remaining questions count
+   */
+  static getRemainingQuestionsCount(): number {
+    const state = this.loadState();
+    if (!state) return 0;
+
+    return state.testCases.length - state.processedQuestionIds.length;
+  }
+}