[Docs] Sync projects.md with Learning Projects implementation

[andrewy1n]

Problem

docs/pages/projects.md still describes Learning Projects as a placeholder, while the live route already includes hero, per-project sections, models, and gallery.

Scope

• Update the Projects doc to match current implementation: routes, file map, and components (ProjectHeroSection, LearningProjectSection, ModelViewer, ProjectGallery).
• Document optional structured fields on LearningProjectSection once [Projects] Extend LearningProjectSection (status, humanoid bridge, links) #169 exists, and MiniAloha once [Projects] Add MiniAloha to Learning Projects page #170 lands.

Acceptance Criteria

• Doc matches App.tsx routes for /projects, /projects/humanoid, /projects/learning-projects, /projects/robocup.
• File paths and responsibilities are accurate.

Files

• docs/pages/projects.md

Related

• Close or refresh after [Projects] Extend LearningProjectSection (status, humanoid bridge, links) #169 / [Projects] Add MiniAloha to Learning Projects page #170 merge.