docs: explain upcoming knowledge wiki and reflection

[cyfyifanchen]

Summary

• Keeps the top README release callout compact while still naming Knowledge Wiki and Dreaming / Reflection as upcoming features.
• Reworks the second section into EverOS: One Memory For All, places the current-state EverOS paragraph above the six highlight cards, and keeps the old three boundary bullets removed.
• Simplifies the positioning table to three columns: Title, EverOS, and Other Agent Memory Libraries.
• Removes the extra paragraph above the comparison table and the small disclaimer below it.
• Clarifies Reflection / Dreaming as idle-or-offline work, not offline-only work.
• Mirrors the same structure and messaging in README.zh-CN.md.

Research Notes

• Checked public positioning/docs across memory-library categories, including API/platform memory, graph/knowledge memory, local recall tools, and file/Markdown-adjacent tools.
• The comparison is intentionally scoped to broad architecture categories and product posture, not absolute claims about individual repos.

Test Plan

• git diff --check
• make docs-check
• make test