Preflight unsupported VS Code runtimes before PDF export

[abdushakoor12]

TLDR

Preflight unsupported VS Code runtimes before markdown PDF export, add a regression test for the early-fail path, and ratchet packages/web coverage thresholds after the passing CI run.

Details

Closes #20.

What was changed:

• Added a new exportPdf regression test that asserts unsupported runtimes fail before markdown is read, HTML is composed, or a PDF is written.
• Added an optional isPrintToPdfRuntimeSupported dependency in the VS Code PDF export path and used it to fail fast with the existing desktop-VS-Code error message.
• Wired the real runtime check in the VS Code extension through vscode.env.uiKind === vscode.UIKind.Desktop.
• Extended the VS Code test mock with UIKind and env.uiKind so the runtime-capability path is testable.
• Updated coverage-thresholds.json for packages/web after make ci passed and the repo’s ratchet step raised those thresholds.

What was added:

• No new runtime dependencies.
• One new regression test covering unsupported PDF-export runtimes.

What was changed/deleted:

• PDF export now rejects unsupported VS Code runtimes before file read/composition work starts.
• No spec/docs were changed.
• No breaking changes.

How Do The Automated Tests Prove It Works?

• make ci passed end-to-end.
• packages/vscode/test/export-pdf.test.ts now includes preflights unsupported runtimes before reading or composing the markdown, which proves the command stops before readFile, createWebviewPanel, and writeFile on unsupported runtimes.
• The full packages/vscode suite passed, including test/export-pdf.test.ts, test/export-pdf-physical.test.ts, and test/extension.test.ts.
• The full web unit and Playwright suites passed during make ci, and the repo ratcheted packages/web coverage thresholds from the measured passing run.