docs: add SolFoundry brand guide (Bounty #852)

[liqiuniu]

Summary

Comprehensive brand guide document for SolFoundry. Bounty #852

---

Contents

1. Brand Essence

• Mission, core values, brand personality

2. Logo

• Variations, clear space, do's/don'ts

3. Color Palette

• Primary colors (Emerald, Purple, Magenta)
• Forge background scale (950-600)
• Text colors
• Status colors
• Tier badge colors
• Gradient definitions

4. Typography

• Font families (Orbitron, Inter, JetBrains Mono)
• Type scale and weights

5. Spacing

• Base unit (4px)
• Border radius scale

6. Components

• Buttons, cards, badges, inputs

7. Imagery

• Photography and illustration guidelines

8. Tone of Voice

• Writing principles with examples

9. Animation

• Defined animations and timing

10. Accessibility

• Color contrast, focus states

11. Assets

• Logo files, favicon, social images

---

Acceptance Criteria

• Color palette with hex codes and usage rules
• Typography specifications with font families
• Logo variations, clearspace, and do's/don'ts

---

Closes #852

Wallet: 7xKXtg2CW87d97TXJSDpbD5jBkheTqA83TZRuJosgAsU