docs: add QQ community group to README (EN + ZH)

[ranxianglei]

Adds a shared QQ community group (1056132097) to both READMEs, per #704.

• README.md: new ## Community section before ## License
• README.zh-CN.md: new ## 社区 section before ## 许可证

One shared group covers all three projects: billion-context, billion-context-pi, opencode-acp — each linked in the section.

Docs-only; no version bump. No code changes, so no typecheck/test/build needed.

[github-actions]

📦 Built Package Artifact

Branch: 2026-09-11_qq-community-readme (1008f2b)

Option A — Install from npm PR tag (recommended)

npm install -g billion-context@pr-705

Each push to this PR publishes a new version under the pr-705 npm tag.

Option B — Download artifact

1. Download the artifact from the Actions run
2. Extract the tarball and install:

tar xzf billion-context-pr705.tgz
npm install -g package

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This comment is automatically updated on each push.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 Received — reviewing PR #705 (docs: add QQ community group 1056132097 to README EN + ZH). Pulling the diff now to verify section placement, EN/ZH parity, and that all three project links are present.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 Review complete — PR #705 looks good.

Verified against #704:

• ✅ README.md: new ## Community section inserted immediately before ## License
• ✅ README.zh-CN.md: matching ## 社区 section immediately before ## 许可证
• ✅ QQ group 1056132097 present in both, bolded, identical value
• ✅ One shared group with all three projects linked — each link verified live (HTTP 200):
  • billion-context, billion-context-pi, opencode-acp
• ✅ Docs-only: 2 files changed, +8 / −0; no code touched, no version bump (package.json untouched)
• ✅ Diff is clean — single hunk per file, no unrelated files, no lockfile/generated artifacts, no whitespace churn
• ✅ No pre-existing Community/QQ section in master (fresh addition, no duplication)
• ✅ Markdown & locale formatting correct (EN em-dash vs ZH fullwidth punctuation, proper heading spacing)
• ✅ Merge state clean (mergeable, rebaseable onto latest master)

No issues found; nothing to fix. Ready for you to merge when convenient — I can't merge the PR myself per project rules.

中文摘要：文档改动无误——两个 README 各新增一个 QQ 群（1056132097）小节，位置（License/许可证之前）、群号、三个项目链接均正确且链接有效，无重复、无代码与版本改动，diff 干净，可以合并。