docs: move QQ community section to top of README

[ranxianglei]

Follow-up to #371 (already merged). That placed the Community/社区 section right before License at the very bottom — easy to miss when landing on the page.

Move it up to be the first content section (right after the header banner, before ## Why?) so the shared QQ group is seen immediately:

• README.md: ## Community now at top
• README.zh-CN.md: ## 社区 now at top

Same content: one shared QQ group (1056132097) covering billion-context, billion-context-pi, opencode-acp. Docs-only; no version bump.

[github-actions]

📦 Built Extension Artifact

Branch: 2026-09-11_readme-qq-top (f6cf612)

Option A — Install from npm PR tag (recommended)

pi install npm:billion-context-pi@pr-372

Each push to this PR publishes a new version under the pr-372 npm tag.

Option B — Download artifact

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

tar xzf billion-context-pi-pr372.tgz
pi install ./package

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This comment is automatically updated on each push.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 On it. Verified #371 is merged into master (6902de4) — the Community/社区 sections currently sit right before License at the bottom of both READMEs. Moving each to be the first ## section (after the header banner + host-support note, before ## Why? / ## 为什么选择 billion-context), content unchanged (QQ Group 1056132097, covers all three projects). Docs-only, no version bump. PR coming shortly.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 Done — PR opened: #373

What changed (branch 2026-09-11_readme-community-top, off master 6902de4 which includes #371):

• README.md: ## Community moved from before ## License to right after the header banner + host-support note, before ## Why? — now the first content section.
• README.zh-CN.md: ## 社区 moved to the same position, before ## 为什么选择 billion-context.
• Content byte-identical, just relocated: one shared QQ group 1056132097 covering billion-context, billion-context-pi, opencode-acp.

Verification: diff is exactly 2 files / 12 insertions / 12 deletions — pure section moves, nothing else touched. No version bump (docs-only), per the issue.

中文摘要:把两个 README 里的 QQ 社区章节从底部(License 前)原样移到页面顶部(横幅之后、Why?/为什么选择 之前),内容未改、无版本号变更,PR #373 已开好,可以合并。