feat(frontend): copy query results as Markdown

[auenger]

Related issue

N/A — this is a small, self-contained frontend enhancement without a linked issue.

Summary

Adds a Markdown table option under the query result selection context menu.

The formatter:

• includes selected data cells and their column titles
• orders cells by grid row and column
• preserves sparse selections as empty cells
• renders nullish values as NULL
• converts line breaks to <br>
• escapes Markdown pipe characters

The new label is localized for English, Chinese, Japanese, Korean, and Spanish. A focused formatter test and package script are included.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • yarn run test:result-markdown — passed
  • yarn run test:i18n — passed
  • focused ESLint over all changed TypeScript and locale files — passed
  • git diff --check — passed
  • Community backend Maven package with Java 17 and tests skipped — 48 modules built successfully
• Manual verification: Community frontend and backend started locally on loopback; GET /api/system through the frontend proxy returned HTTP 200.
• UI evidence: N/A — no browser automation instance was available in the local environment.

Risk and compatibility

• Public API or stored data: N/A; clipboard-only frontend behavior.
• Database or driver compatibility: N/A.
• Network, privacy, or security: No new network calls; selected result values are copied only through the existing clipboard utility.
• Community / Local / Pro boundary: Implemented in the Community frontend.
• Backward compatibility: Additive context-menu item; existing copy formats are unchanged.

Reviewer map

• Start here: markdownTable.ts for formatting rules, then onContextmenuCell/index.ts for menu integration.
• Failure condition: Incorrect ordering or escaping could produce malformed Markdown for sparse or multiline selections.
• Rollback or disable path: Remove the markdownTable context-menu entry and its formatter/handler.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: OpenAI Codex assisted with implementation and test drafting; the changes were reviewed and verified locally.

[openai0229]

Thanks for the contribution. There are two potential issues worth checking before merging:

1. Backslash followed by a pipe may break the generated table

   For a cell value such as left\|right, the current formatter produces left\\|right. In GFM, the two backslashes resolve to a literal backslash, leaving the pipe to act as a column separator. This can shift columns or drop subsequent values.

   Could you verify this case? One possible fix is to escape backslashes before escaping pipes:

   .replace(/\\/g, "\\\\")
   .replace(/\|/g, "\\|")

   It would also be useful to add a regression test covering \|.

2. The new test script does not appear to run in CI

   test:result-markdown was added to package.json, but the frontend CI workflow runs each test script explicitly and does not currently invoke this one. Could you add a corresponding step to .github/workflows/ci.yml?

The existing formatter test, i18n validation, ESLint, and Community Web build otherwise passed in my local review.