docs: add quick-start guide for engineers

[faisalnugroho]

Summary

Adds a comprehensive quick-start guide section to the README that helps engineers quickly find and use the right brand assets.

Fixes #75, #77, #78, #80, #82

What's included

Format Selection Guide — When to use SVG vs PNG vs EPS based on context (web UI, email, print, social media).

Logo Variant Selection — Clear table showing which logo variant to use for light, dark, colorful, and blue-themed backgrounds.

Sizing Guidelines — Minimum and recommended sizes for common contexts (favicon, app icon, nav bar, hero, social media).

Social Media Usage — Recommendations for profile pictures, post images, and story overlays.

File Naming Convention — Explanation of the Base_[variant]_[color].[format] pattern used across all assets.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[faisalnugroho]

Hi! Following up on this docs PR. This PR adds a quick-start guide for engineers covering logo file formats, sizing rules, color specs, and HTML/CSS code examples. Fills the gap between the existing brand guidelines and practical developer usage.

All CI checks pass (StepSecurity ✅). Would love to get your review when you have a moment. Thanks!