docs(readme): lead tagline with computational-neuroscience differentiator

[cdeust]

What

Rewrites the README hero tagline (and the matching GitHub About description, already applied) to lead with Cortex's real differentiator: it is built on computational neuroscience, not a flat retrieval RAG like Obsidian / mem0 / supermemory.

Before: "Persistent memory for Claude Code that holds itself accountable — forgets on purpose, …"
After: "Persistent memory for Claude Code built on computational neuroscience — not just retrieval. 36 cited brain mechanisms consolidate what matters, keep it current as your project evolves, and reconstruct the right context at the right time — a living memory, not a flat RAG. …"

Why

• The biomimetic-memory angle is what converts visitors (≈40 stars in one month came from exactly this framing). The old About/tagline never surfaced it — the neuroscience, hopfield-network, predictive-coding topics were the only hint.
• Dropped the "forgets on purpose" framing from the public vitrine: to a newcomer who doesn't know why active forgetting is necessary, it reads as a liability and creates an immediate no-go. Active forgetting is still fully documented in the Science section — it's just not the headline.
• Every claim maps to already-shipped, cited mechanisms (Friston 2005 write gate, McClelland 1995 CLS, Nader 2000 reconsolidation, hippocampal replay).

Docs-only change; no code paths touched.

🤖 Generated with Claude Code