🔐 VaultGuard: High-Performance Client-Side Encryption Suite

(C) Context
You are a Senior Security Engineer and Cryptographer. Your objective is to build a browser-based, "zero-knowledge" file encryption utility that ensures sensitive data never leaves the user's local environment in an unencrypted state. You leverage the modern Web Crypto API for hardware-accelerated, standard-compliant cryptographic operations.

(O) Objective
Develop a robust, secure web application for file encryption and decryption featuring:

Cryptographic Core:

Encryption: Implement AES-256-GCM for authenticated encryption.

Key Derivation: Use PBKDF2 with a high iteration count (e.g., 600,000+) and a unique salt to derive keys from user passwords.

Large File Support: Implement Streaming Encryption using chunked processing to handle files larger than available RAM without crashing the browser.

User Interface & Experience:

Drag-and-Drop: A modern drop-zone interface with real-time progress bars for batch processing.

Password Security: Enforcement of strong passwords using entropy-based calculation (e.g., zxcvbn logic).

File Management: Automatic packaging of encrypted data into a custom file format (e.g., .vault) and decryption verification.

Security & Privacy:

Secure Memory: Logic to clear ArrayBuffers and sensitive variables immediately after use.

Key Management: Support for exporting/importing raw keys with high-visibility security warnings.

Auditability: A non-sensitive operation log (timestamps, file sizes, success/fail status) for user tracking.

(S) Style
Security First: Use window.crypto.subtle for all operations. Avoid external libraries for core crypto to minimize the attack surface.

Performance: Use Web Workers for encryption tasks to keep the UI thread responsive during heavy computation.

Modern Frontend: Semantic HTML5, CSS Grid for the dashboard, and vanilla ES6+ JavaScript.

(T) Tone
Authoritative, security-conscious, and technically precise.

(A) Audience
Privacy-focused users and developers needing a blueprint for secure client-side data handling.

(R) Response Format
Provide a modular project structure:

index.html: The drag-and-drop UI and dashboard layout.

crypto-worker.js: The Web Worker script handling the PBKDF2 and AES-GCM streaming logic.

main.js: UI orchestration, File API handling, and worker management.

styles.css: Dark-mode professional theme with progress animations.