cdc: add more usage caution about the table route

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Summary by CodeRabbit

• 文档
  • 更新 TiCDC 表路由文档，明确分库场景下 DML、表级 DDL 与库级 DDL 的处理规则。
  • 补充被事件过滤的 DDL、默认目标库冲突检查及删库改写行为说明。
  • 扩展合库配置示例，新增事件过滤规则与删除目标库风险警告。

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ℹ️ Recent review info

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Plan: Advanced

Run ID: 6b684eb8-cdd2-41d6-b306-32e9eb23b3b5

📥 Commits

Reviewing files that changed from the base of the PR and between 924e58f and e31e55d.

📒 Files selected for processing (1)

• ticdc/ticdc-table-routing.md

Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review.

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📝 Walkthrough

Walkthrough

更新 TiCDC 表路由文档，明确分库对 DML、表级 DDL 和库级 DDL 的处理方式，并补充合库场景的事件过滤配置与删库风险。

Changes

表路由规则与风险说明

Layer / File(s)	Summary
分库与合库路由说明 ticdc/ticdc-table-routing.md	明确分库仅适用于 DML 和表级 DDL。说明库级 DDL 不会拆分为多个目标库操作，被过滤的 DDL 仍参与路由处理。补充默认目标库和 DROP DATABASE sales 的示例。合库示例新增 sales.*、crm.*、finance.* 的事件过滤配置，并警告未过滤的删库事件会删除整个目标库。

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to e31e5

The documentation-only change adds supported routing cautions and filtering guidance without an identified current risk to users or deployments.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	描述包含贡献者协议、目标版本和其他模板章节，但必填的“ What is changed, added, or deleted? ”章节为空，未说明具体修改内容和原因。	补充变更内容和修改原因。请说明 TiCDC 表路由文档新增了哪些分库、合库及库级 DDL 使用注意事项，并说明这些变更适用的场景。

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	标题与变更内容相关，明确说明为表路由新增使用注意事项。表述简洁，能够概括主要变更。

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