Prebid 11: document TypeScript-first policy for new source files

AGENTS.md

@@ -21,6 +21,7 @@ This file contains instructions for the Codex agent and its friends when working
 
 ## General guidance
 - Node.js `>=20` is required; dependencies are managed with `npm`.
+- Whenever possible, all new files added under `/modules`, `/libraries`, and `/src` must be TypeScript files (`.ts`) instead of JavaScript files (`.js`).
 - Added or modified code must have at least 80% unit test coverage.
 - Link any required documentation PRs in the PR description.
 - Avoid modifying files in `node_modules` or generated build artifacts under `build`.

CONTRIBUTING.md

@@ -6,6 +6,8 @@ master branch.
 Pull requests must have 80% code coverage before being considered for merge.
 Additional details about the process can be found [here](./PR_REVIEW.md).
 
+Whenever possible, all new files added under `/modules`, `/libraries`, and `/src` should be authored as TypeScript (`.ts`) rather than JavaScript (`.js`).
+
 There are more details available if you'd like to contribute a [bid adapter](https://docs.prebid.org/dev-docs/bidder-adaptor.html) or [analytics adapter](https://docs.prebid.org/dev-docs/integrate-with-the-prebid-analytics-api.html).
 
 ## Issues

PR_REVIEW.md

@@ -19,6 +19,8 @@ General gulp commands include separate commands for serving the codebase on a bu
 
 ### General PR review Process
 
+- Whenever possible, all new files added under `/modules`, `/libraries`, and `/src` should be TypeScript files (`.ts`) rather than JavaScript files (`.js`).
+
 - All required global and bidder-adapter rules defined in the [Module Rules](https://docs.prebid.org/dev-docs/module-rules.html) must be followed. Please review these rules often - we depend on reviewers to enforce them.
 - Checkout the branch (these instructions are available on the GitHub PR page as well).
 - Verify PR is a single change type. Example, refactor OR bugfix. If more than 1 type, ask submitter to break out requests.