Improve test failure handling

[millerds]

Change Description:
Improve tests to handle more error cases and improve ts vs js seperation

1. Do these changes impact any npm scripts commands (in package.json)? (e.g., running 'npm run start')
   No.

2. Do these changes impact VS Code debugging options (launch.json)?
   No.

3. Do these changes impact template output? (e.g., add/remove file, update file location, update file contents)
   No.

4. Do these changes impact documentation? (e.g., a tutorial on https://docs.microsoft.com/en-us/office/dev/add-ins/overview/office-add-ins)
   No.

If you answered yes to any of these please do the following:
> Include 'Rick-Kirkham' in the review
> Make sure the README file is correct

Validation/testing performed:
Ran automated tests.

[Copilot]

Pull request overview

This PR improves the reliability of the test harness by adding clearer failure reporting/timeouts for end-to-end tests and reorganizing TypeScript vs JavaScript tooling/config to better isolate test-only TypeScript.

Changes:

• Add explicit timeout + “test-error” result handling to surface add-in initialization failures in E2E tests.
• Split TypeScript configuration for tests (test/tsconfig.json) and add jsconfig.json for JS/JSX editor tooling.
• Switch Mocha execution/debugging to a repo-local ts-node registration script and add a test typecheck script.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
tsconfig.json	Replaces root TS config with a test-only config via extends/include.
test/unit/word.test.ts	Refactors Word mock typing for stricter TS checks.
test/unit/powerpoint.test.ts	Adds explicit mock types for PowerPoint unit tests.
test/unit/excel.test.ts	Refactors Excel mock context and callback typing.
test/tsconfig.json	Introduces strict TypeScript config scoped to tests.
test/register-ts-node.js	Adds a custom ts-node registration pointing at the test tsconfig.
test/end-to-end/ui-test.ts	Adds timeout + error-result handling when collecting E2E results.
test/end-to-end/src/test.index.tsx	Adds init error reporting to the taskpane test entrypoint.
test/end-to-end/src/test-helpers.ts	Adds structured test result helpers + richer error formatting.
test/end-to-end/src/host-tests.ts	Improves E2E host tests by awaiting Office.run calls and sending error results on failure.
package.json	Updates test scripts to use the custom ts-node register; adds typecheck:test.
jsconfig.json	Adds JS/JSX project config to distinguish JS vs TS projects.
convertToSingleHost.js	Ensures jsconfig.json is removed by the single-host conversion script.
.vscode/launch.json	Updates Mocha debug configs to use the custom ts-node register script.
.npmrc	Changes the npm registry to a Microsoft feed proxy.

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