fix(clipboard): preserve Windows line endings for result copies

[openai0229]

Related issue

N/A

Summary

Windows native applications such as SAP GUI expect clipboard text rows to use CRLF. Result-set copies previously wrote LF-only text, which caused SAP paste to collapse rows and display # markers. Normalize copied text to CRLF on Windows while preserving LF on macOS/Linux, and normalize internal result-grid matching so table paste keeps its cell metadata.

Affected surfaces

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

Verification

• Commands and results:
  • yarn install --frozen-lockfile --non-interactive — passed in the PR worktree.
  • yarn test:sql-in-clipboard — passed (clipboard normalization, internal grid clipboard, SQL-in clipboard, insert defaults).
  • yarn lint — passed (ESLint and Stylelint).
  • git diff --check — passed.
  • Before PR creation, Community frontend build, Local frontend build/API contract, Local backend packaging, and browser VTable clipboard regression all passed.
• Manual verification: Local Windows runtime was tested with SAP; result-set paste now works with rows preserved.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: N/A; clipboard serialization only.
• Database or driver compatibility: N/A; no database code changed.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: Shared Community frontend utility; Studio consumes the pinned Community source.
• Backward compatibility: macOS/Linux retain original line endings; internal grid paste accepts LF and CRLF.

Reviewer map

• Start here: chat2db-community-client/src/utils/clipboardText.ts and chat2db-community-client/src/utils/index.ts:292-325.
• Failure condition: On Windows, result-set copy must contain \\r\\n between rows; internal result-grid paste must still recover the original matrix.
• Rollback or disable path: Revert commit 34f061f56 to restore the previous clipboard serialization.

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: Codex performed source investigation, implementation, tests, browser regression verification, and packaging validation under maintainer direction.