docs: align test sharding instructions with package.json

Updates `README.md` and `CONTRIBUTING.md` to explicitly mention the availability of `test:unit:shard1`, `shard2`, and `shard3`, ensuring the documentation accurately reflects the sharding configuration defined in `package.json`. This provides developers with clear options for running subsets of unit tests.

Co-authored-by: PR0M3TH3AN <[email protected]>

CONTRIBUTING.md

@@ -41,7 +41,7 @@ Automated agents contributing to this repository should follow these rules:
 - **Commit Messages**: Use the convention `type(scope): description (agent)` (e.g., `fix(ai): formatting (agent)` or `docs(ai): update quickstart (agent)`).
 - **Reference Issues**: Link to relevant issues in the PR description.
 - **Review AGENTS.md**: Always consult `AGENTS.md` for specific architectural guidelines (like URL-first playback, token-first design system) and constraints before starting work.
-- **Efficiency**: Prefer running targeted or sharded tests (e.g., `npm run test:unit:shard1`) to conserve resources during iteration.
+- **Efficiency**: Prefer running targeted or sharded tests (e.g., `npm run test:unit:shard1`, `shard2`, or `shard3`) to conserve resources during iteration.
 
 ## Submitting a Pull Request
 
@@ -122,7 +122,7 @@ To set up the project locally:
    npm run test:unit
    ```
 
-   _Note: Running the full suite (`npm run test:unit`) is resource-intensive, runs sequentially, and may time out in some environments. We strongly recommend using sharded runs for local development to save time: `npm run test:unit:shard1`._
+   _Note: Running the full suite (`npm run test:unit`) is resource-intensive, runs sequentially, and may time out in some environments. We strongly recommend using sharded runs for local development to save time: `npm run test:unit:shard1`, `shard2`, or `shard3`._
 
    You can also run end-to-end and visual tests:
 

README.md

@@ -182,7 +182,7 @@ See [`CONTRIBUTING.md`](./CONTRIBUTING.md) for the full developer guide.
 
 **Verify your work:**
 
-- **Run unit tests**: `npm run test:unit` (Required before PRs). _Tip: Use `npm run test:unit:shard1` for faster local feedback._
+- **Run unit tests**: `npm run test:unit` (Required before PRs). _Tip: Use `npm run test:unit:shard1`, `shard2`, or `shard3` for faster local feedback._
 - **Format code**: `npm run format` (Required before PRs)
 - **Lint code**: `npm run lint` (Checks for CSS, hex colors, inline styles)