fix: refresh extension debug builds and source maps

[renkun-ken]

F5 launched the extension without rebuilding it, and the debugger still searched out/src even though esbuild now writes the extension bundle to dist. Build the extension and webviews before launching, point source maps at the generated bundle, and compile both the bundle and test files before extension tests. The new npm run compile command lets debugging build the JavaScript assets without installing the bundled R package.

Document the activation prerequisites and the workaround for VS Code 1.139's separate debugger attachment regression (upstream issue). That regression requires the fixed Microsoft debugger; the repository configuration changes address the build and source-map issues.

Validation:

• npm run pretest passed (esbuild bundle and TypeScript compilation).
• Checked all launch configurations for valid build tasks and bundle paths; git diff --check passed.
• An isolated VS Code 1.139.1 session with Microsoft's JavaScript Debugger Nightly 2026.9.2317 hit the TypeScript breakpoint in activate() at src/extension.ts:44, resumed, and successfully activated the development extension and registered its R commands.