docs(readme): refresh banner and localized quickstarts

[cyfyifanchen]

Summary

• Replace the English and Chinese README banner with the compressed GitHub User Content asset previewed below.
• Keep provider onboarding localized, following the existing main split:
  • English README.md and QUICKSTART.md: one OpenRouter key with explicit keyword search.
  • Chinese README.zh-CN.md: one Bailian / DashScope key reused for [llm], [embedding], and [rerank], with hybrid search.
• Remove the leading 0. from the English Prerequisites and Chinese 前置条件 headings.
• Keep the standalone everos demo before initialization and clearly separate it from the real server-backed flow and everos demo --live.

Area

• Architecture method
• Benchmark
• Use case
• Documentation
• Developer experience
• CI, build, or release

Verification

make docs-check
uv run pytest tests/integration/test_tiers/test_tier1_keyword_only.py -q
make ci

All commands passed on commit 4750a72.

Checklist

• I kept the change scoped to the relevant area.
• I am opening this from a separate branch, not pushing directly to main.
• I updated docs, examples, or setup notes when behavior changed.
• I added or updated tests when the change affects behavior.
• I did not commit secrets, .env files, dependency folders, or generated output.
• Active relative links in Markdown files resolve.

Notes for Reviewers

• Bailian is intentionally absent from the English onboarding; OpenRouter is intentionally absent from the Chinese onboarding.
• OpenRouter Tier 1 needs only [llm], but searches must explicitly set "method": "keyword" because the API default is hybrid and requires embedding.
• The Chinese Bailian setup reuses one DashScope key across qwen-plus, text-embedding-v4 (dimensions = 1024), and gte-rerank-v2 (provider = "dashscope").
• Plain everos demo is hardcoded and local: it needs no key, does not call the server, and does not modify the real memory root. everos demo --live is separate and requires a running server with embedding configured.

Banner preview