docs(knowledge): replace dead data-flow.md link with Auto-Sync section

[dvd233]

Description | 描述

Fixes #1263.

MemoryKnowledge/README.md pointed Auto-Sync readers at docs/data-flow.md §9, but that file has never existed in the repository (verified via commit history on both feat/server_team and main), so the relative link was dead and the Auto-Sync configuration was undiscoverable.

Change (option 2 from the issue — replace the dead link with valid documentation):

• The capability-table entry now points to a new 「可选：Auto-Sync」 README section (same style as the existing ClickHouse / Langfuse optional sections).
• The new section documents, all verified against src/store/auto-sync-scheduler.ts and src/routes/auto-sync.ts:
  • KNOWLEDGE_AUTO_SYNC_ENABLED (default false)
  • KNOWLEDGE_AUTO_SYNC_SCAN_INTERVAL_MIN (default 10, clamped to 1–60)
  • KNOWLEDGE_AUTO_SYNC_MAX_CONCURRENT (default 3, clamped to 1–20)
  • first scan delayed 30 s after start
  • manual POST /v3/auto-sync/trigger is a no-op while disabled (returns triggered: false)

Related Issue | 关联 Issue

Fixes #1263

Change Type | 修改类型

• Documentation update | 文档更新

Self-test Checklist | 自测清单

• Verified locally | 本地验证通过
• No existing features affected | 无影响现有功能

Additional Notes | 其他说明

• Acceptance criteria from the issue: no broken relative link remains (the data-flow.md reference is gone); the README now explains the enable switch, interval, concurrency, startup delay, and manual-trigger behaviour.
• Checked the other relative Markdown links in this README (../MemoryPanel/, ../deploy/panel-knowledge-combined/README.md) — both resolve.

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This PR was prepared with AI coding assistance; the verification (dead-link reproduction, source-of-truth values, link check) was run locally by me. 本 PR 在 AI 编码助手辅助下完成，验证均由本人本地执行。

[yangjj-iso]

LGTM

[Maxwell-Code07]

Thank you so much for your attention and contribution! We will arrange an internal review for this PR shortly, and all feedback will be shared right here in the discussion.