docs: update website copy — sessions lasting days, crystal-clear memory (#442)

## Summary

Updates the landing page copy to reflect the mega-session benchmark
results and stronger value proposition.

## Changes

### Hero section
- Description: emphasizes "crystal-clear memory across sessions lasting
days, hundreds of turns, any LLM provider"
- Chip: "400K+ Token Sessions" → "Sessions Lasting Days"

### Stats strip
Already updated in #440: +70% vs compaction, 13/20 perfect scores, 2.3M+
tokens tested.

### "The Problem" section
- Compaction step: now cites the real 2.3M-token benchmark — "compaction
reduces 2.3 million tokens to an 11K summary, scoring 2.4/5. Lore scores
4.0/5."

### "The Solution" section
- Recall step: "13 out of 20 perfect recall scores where compaction
managed 5"

### Feature cards
- Cost card: "Infinite sessions, lower cost" → "Sessions as long as you
want" — "Work for days, hundreds of turns, millions of tokens — memory
stays sharp."
- Compatibility card: "Works with any provider" → "Portable memory, any
provider" — "Switch providers, switch tools, switch machines — your
memory travels with you."

### Ticker
- Lead with "2.3M tokens, 5 days, crystal-clear recall" + scores
- Added "Any provider, any tool — Portable memory that travels with you"
- Replaced "Compaction destroys details" (negative) with real benchmark
numbers (positive proof)