feat: add interactive Calcifer graph hero

[ytvee]

Summary

Implements the single requested landing-page hero section and no additional sections.

• initializes a minimal Astro + TypeScript static site;
• keeps the headline, description, actions and technology labels in server-rendered HTML;
• renders a fire-demon silhouette entirely from connected nodes and edges;
• adds Obsidian-like drag behavior with connected-node spring propagation;
• reveals a dim code wall with a pointer-speed-driven torch effect while dragging;
• lazy-loads Three.js after idle time or the first interaction;
• includes responsive quality tiers, reduced-motion behavior and a deterministic SVG fallback;
• adds focused graph/physics tests, CI and animation architecture documentation.

Rendering and performance

• one THREE.Points draw call for nodes;
• one THREE.LineSegments draw call for edges;
• custom point shader for glow instead of a post-processing pipeline;
• custom target-anchor and neighbour-spring physics so the face and flame silhouette recover after dragging;
• capped device pixel ratio and adaptive node count;
• animation pauses while the document is hidden and GPU resources are disposed on disconnect.

Verification

• npm test — 6 tests passed;
• npm run build — Astro check passed with 0 errors, 0 warnings and the static production build completed.

Closes #1

[ytvee]