docs: update eval results — context retention 3.9→4.6, +77% vs tail-window

[BYK]

Updates marketing copy with the latest eval results from the recall quality + distillation transparency work (#428, #430, #431, #432, #433, #434).

README.md

• Context retention table: Medium 2.3→4.1, Hard 3.3→4.8, Average 3.9→4.6
• Lore vs tail-window delta: +50%→+77%
• Added footnote: Lore scores averaged across multiple runs; TW/compaction baselines from a prior eval run with the same scenarios
• Added v6 to version history

docs/index.html

• Hero stat: +50%→+77% vs tail-window
• Detail retention: 4.8→4.6 (overall average across difficulty levels, multiple runs)

Review corrections

• Fixed Medium from 4.3→4.1 (honest multi-run average, not cherry-picked)
• Average row (4.6) now self-consistent with column values: (5.0+4.1+4.8)/3=4.63≈4.6
• Added footnote clarifying that TW/compaction columns are from a prior eval run