Act as a principal full-stack software engineer and startup product designer.

I want you to build a production-ready MVP for the following digital product:

=========================================
PRODUCT SPECIFICATION: FOCUSSPRINT AMBIENT OS
=========================================
• Concept: Minimalist Pomodoro timer bundled with generative brown noise and distraction-free task staging.
• Category: Productivity
• Target Audience: Writers, solo coders, and deep-work enthusiasts.
• Core Problem Being Solved: Standard timer apps are cluttered with complex project management features that break flow state.
• Primary Monetisation Model: $12 lifetime purchase for custom themes and sound generator packs.
• Target Build Timeframe: 1 Weekend (Difficulty: Easy)

CORE FEATURES TO IMPLEMENT IN V1.0:
1. Single-task focus card that occupies entire view
2. Dynamic ambient sound mixer (Rain, Cafe, Brown Noise)
3. Strict "Don’t touch your phone" challenge mode
4. Session completion streak ledger
5. Local offline playback with zero tracking

PREFERRED TECHNOLOGY STACK:
• Single File HTML/Tailwind/JS

UI & DESIGN REQUIREMENTS:
• Clean, modern SaaS aesthetic with balanced typography (Inter / Plus Jakarta Sans).
• Responsive layout prioritizing mobile-first and desktop workflows.
• Thoughtful empty states, clear visual hierarchy, accessible touch targets, and subtle micro-animations.
• Dark and light mode compatibility.

DELIVERABLE:
Please provide:
1. Architecture outline (state management, component tree, and storage schema).
2. The complete, fully-commented, production-ready code ready to run immediately.
3. Next steps for launching and onboarding the first 10 paying customers.