feat: add schema dump command for AI database discovery

[zx06]

概述

新增 xsql schema dump 命令，导出数据库结构信息（表、列、类型、约束、索引），供 AI/agent 自动理解数据库 schema。

变更内容

新增功能

• xsql schema dump 命令，支持导出数据库结构
• 支持 MySQL 和 PostgreSQL
• 输出包含：表、列、索引、外键
• 支持表名过滤（通配符 * 和 ?）
• 支持 JSON/YAML/Table 输出格式

文件变更

文件	说明
internal/db/schema.go	Schema 数据结构和接口
internal/db/mysql/schema.go	MySQL schema 提取实现
internal/db/pg/schema.go	PostgreSQL schema 提取实现
cmd/xsql/schema.go	CLI 命令实现
internal/output/writer.go	Table 格式化支持
internal/app/app.go	Tool spec 更新
docs/rfcs/0005-schema-dump.md	RFC 设计文档
docs/cli-spec.md	CLI 规范更新
docs/ai.md	AI 集成文档更新
README.md	项目说明更新

测试

• ? 单元测试：internal/db/schema_test.go
• ? E2E 测试：tests/e2e/schema_test.go（8 个测试用例）

使用示例

# 导出所有表结构
xsql schema dump -p dev -f json

# 过滤特定表（支持通配符）
xsql schema dump -p dev --table "user*"

# 包含系统表
xsql schema dump -p dev --include-system

输出示例

{
  "ok": true,
  "schema_version": 1,
  "data": {
    "database": "mydb",
    "tables": [
      {
        "schema": "public",
        "name": "users",
        "columns": [
          {"name": "id", "type": "bigint", "primary_key": true},
          {"name": "email", "type": "varchar(255)", "nullable": false}
        ]
      }
    ]
  }
}

相关文档

• RFC: docs/rfcs/0005-schema-dump.md
• CLI 规范: docs/cli-spec.md
• AI 集成: docs/ai.md

[codecov]

Codecov Report

❌ Patch coverage is 79.54545% with 108 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.76%. Comparing base (2f2688d) to head (d32d5eb).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
internal/db/pg/schema.go	81.33%	21 Missing and 21 partials ⚠️
internal/db/mysql/schema.go	79.51%	17 Missing and 17 partials ⚠️
cmd/xsql/schema.go	55.55%	25 Missing and 3 partials ⚠️
internal/db/schema.go	92.30%	1 Missing and 1 partial ⚠️
internal/output/writer.go	94.73%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #28      +/-   ##
==========================================
+ Coverage   79.02%   80.76%   +1.74%     
==========================================
  Files          32       36       +4     
  Lines        1864     2392     +528     
==========================================
+ Hits         1473     1932     +459     
- Misses        326      357      +31     
- Partials       65      103      +38     

Flag	Coverage Δ
e2e	44.98% <70.10%> (-3.66%)	⬇️
integration	44.98% <70.10%> (-3.66%)	⬇️
unittests	66.26% <19.50%> (-12.50%)	⬇️

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[sonarqubecloud]

Quality Gate failed

Failed conditions
14.2% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud