docs: introduce Scout mascot and rewrite README

[GeoGeekLab]

Refresh the repository presentation around the new Scout mascot.

What changed

• add two optimized Scout mascot assets under docs/assets/mascot/;
• add docs/MASCOT.md with the visual/usage system;
• rewrite README end-to-end in a more GitHub/open-source style;
• match the GeoDebug-style opening rhythm: title, tagline, short description, badges, nav, mascot;
• replace the old long-form manifesto/boundary-heavy copy with concise technical sections;
• use different Scout poses in the README header and development section;
• remove the obsolete geo-task-intelligence.svg workflow illustration;
• keep the current install, task, provider, planning, replay, release, and development commands aligned with v0.5.0.

No runtime code changes.