Fix lint tooling and move to Node 22 #124

Why: npm test runs lint first (pretest), and ESLint 7 with @typescript-eslint 4 fails on every file with Parsing error: DeprecationError: 'originalKeywordKind' has been deprecated. No test can run until this is fixed. The current Vitest and @vscode/test-electron releases need Node 22, and CI uses Node 20.

What:

• Move to ESLint 9+ with a flat eslint.config.mjs and typescript-eslint 8.
• Take lint out of pretest; it becomes its own CI step.
• Remove unused devDependencies (ftp, rimraf, mkdirp, get-port, old vsce), and use @vscode/vsce.
• Use Node 22 in publish.yml.
• Remove the test script that points at the missing out/test/runTest.js.

Done when: npm run lint passes locally.

References:

• The official yo code generator ships eslint.config.mjs (flat config): https://github.com/microsoft/vscode-generator-code/blob/main/generators/app/templates/ext-command-ts/eslint.config.mjs