docs: add comprehensive SolFoundry Brand Guide

[zengbinli]

Bounty: SolFoundry Brand Guide Document

Bounty: #852 | Reward: 500K $FNDRY | Tier: T2 | Domain: Creative

---

What This PR Delivers

A comprehensive brand guide document extracted directly from SolFoundry's existing codebase and design system.

How It Was Built

All brand values were extracted from actual source code, not invented:

1. Logo colors — Analyzed assets/logo-full.svg (extracted #14F195, #9945FF, #FFD700)
2. Design system colors — Extracted from frontend/src/index.css CSS custom properties
3. Tailwind theme — Parsed from frontend/tailwind.config.js
4. Typography — Font families and weights from Tailwind config (Orbitron, Inter, JetBrains Mono)
5. Brand identity — Derived from README mission statement and project positioning

Contents

Section	Description
Brand Overview	Mission, personality, positioning
Logo	Files, colors, clearspace, variations, misuse
Color Palette	40+ colors with hex, RGB, rgba, and usage rules
Typography	3 font families, 7 weights, 10-step type scale
Imagery Guidelines	Photography, illustration, icon, animation
Tone of Voice	Writing guidelines with do's/don'ts and microcopy
Design Principles	5 core principles (dark-first, glow, animation, a11y, responsive)
Component Examples	CSS code for buttons, cards, badges
Do's and Don'ts	Visual reference tables

Acceptance Criteria Met

• Color palette with hex codes and usage rules
• Typography specifications with font families
• Logo variations, clearspace, and do's/don'ts
• Imagery guidelines
• Tone of voice documentation
• Design principles

---

Wallet: 3D2uVzAsGhrWfUprHLwezCNkE1u9eK7SH2MAhbC3gFVN