feat: redesign landing page with coherent narrative + visual upgrades

Sections: Hero → Two Paths (Human/Agent cards with glow) → Pipeline Track
(8-step flow with L1/ER/PER layer tags) → Why TaskForest (6 differentiators)
→ Architecture (3-layer: L1, ER, PER) → CTA

Visual: consistent green=L1, amber=ER, purple=PER color system throughout,
card hover effects, glow orbs, pipeline legend

Author: jimmdd