fix(knowledge): accept SQL uploads and route them through MarkItDown

[dvd233]

Description

Accept SQL files throughout the knowledge-upload path and parse them as text with the existing MarkItDown engine. The Go upload whitelist previously rejected .sql before DocReader was reached; DocReader also lacked the SQL routing entry.

• Add SQL to the shared Go upload/import whitelist and the frontend fallback whitelist used before parser metadata loads.
• Route empty or builtin engine requests for SQL through MarkItDown and allow explicit MarkItDown requests.
• Cover the upload service through storage and document-task enqueueing, dynamic frontend whitelist behavior, parser routing and actual SQL text extraction.

SQL statements are read as document text, not executed.

Type of Change

• Bug fix
• Test
• Breaking change

Related Issue

Fixes #3494

Testing

• Focused Go upload/import regressions: 45 tests and subtests passed after merging main bccb4b1 (Go 1.26.5, desktop build tag, GCC 15 UCRT toolchain), including .sql and .SQL uploads into DocumentProcess without a spreadsheet-summary task.
• Frontend file-type regressions: 4 passed (including the current-main XMind regression); changed utility strict TypeScript check passed.
• Python parser routing and actual SQL text extraction: 10 passed.
• Changed-scope golangci-lint 2.13.2: 0 issues (CI uses 2.12.2); gofmt and git diff --check passed.
• The earlier full DocReader run exercised 199 tests with one environment error because the Playwright WebKit executable was absent. It was not rerun for the Go/frontend whitelist follow-up. Full frontend vue-tsc --build and a deployed HTTP/gRPC/database end-to-end environment were not run locally.

Checklist

• Changes are limited to SQL file admission, parser routing and regressions.
• Changed source files are formatted and targeted tests pass.
• Local verification limits are documented above.
• Self-reviewed the final diff and verification evidence.
• Breaking changes (none).

This PR was prepared with AI assistance. Screenshots are not applicable to this file-admission and parser-routing change.

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[lyingbug]

Go 侧的上传白名单里没有 sql，上传直接被拒，这个改动端到端不起作用

[dvd233]

已在 8fd9535 补齐 Go 共享上传/导入白名单中的 sql，并同步前端 parser 元数据尚未加载时的默认白名单。新增回归从 CreateKnowledgeFromFile 实际入口验证 .sql / .SQL 可保存并进入 DocumentProcess 队列，同时保留 Python 的实际 SQL 文本提取测试。Go 相关 44 项测试/子用例、前端 3 项、Python 10 项通过，差异范围 golangci-lint 为 0 issues。SQL 仅作为文本知识文档解析，不执行其中的语句。

[dvd233]

Current-head CI follow-up for cd674830: the DocReader job is cancelled, not passed. In run 36898338243, dependency installation and Python compilation succeeded, but Install Playwright WebKit spent almost the entire 30-minute job budget installing system packages. The Python and Go client test steps were never reached. Other applicable current-head checks succeeded.

The completed local frontend, parser and Go checks remain recorded in the test plan; they do not replace this incomplete integration job. Could a maintainer rerun the cancelled DocReader job? I have no upstream Actions write permission and have not changed assertions or workflow time limits in this PR.