Add Copilot workspace setup and agent documentation (#287)

* Add copilot setup steps workflow file

Co-authored-by: Hexagon <419737+Hexagon@users.noreply.github.com>

* Add AGENTS.md with project structure and contribution guidelines

Co-authored-by: Hexagon <419737+Hexagon@users.noreply.github.com>

* Update AGENTS.md with complete test file listing

Co-authored-by: Hexagon <419737+Hexagon@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Hexagon <419737+Hexagon@users.noreply.github.com>

Author: Copilot

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,48 @@
+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # If you want to clone the repository as part of your setup steps, for example to install dependencies, you'll need the `contents: read` permission. If you don't clone the repository in your setup steps, Copilot will do this for you automatically after the steps complete.
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v5
+
+      - name: Setup Deno
+        uses: denoland/setup-deno@v2
+        with:
+          deno-version: v2.x
+          cache: true
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "lts/*"
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Cache dependencies
+        run: deno install

AGENTS.md

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+# Croner - Agent Guide
+
+## Project Overview
+
+Croner is a lightweight, zero-dependency cron library for JavaScript and TypeScript that works across Node.js, Deno, Bun, and browsers.
+
+## Project Structure
+
+```
+croner/
+├── src/                  # Source code
+│   ├── croner.ts        # Main entry point
+│   ├── pattern.ts       # Cron pattern parser
+│   ├── date.ts          # Date handling utilities
+│   ├── options.ts       # Configuration options
+│   └── helpers/         # Helper utilities
+├── test/                # Test files
+│   ├── croner.test.ts
+│   ├── pattern.test.ts
+│   ├── options.test.ts
+│   ├── range.test.ts
+│   ├── stepping.test.ts
+│   └── timezone.test.ts
+├── build/               # Build scripts
+├── docs/                # Documentation
+└── deno.json            # Deno configuration and tasks
+```
+
+## Standards Compliance
+
+This project aims to follow the **OCPS (Open Cron Pattern Standard)** drafts available at [github.com/open-source-cron/ocps](https://github.com/open-source-cron/ocps).
+
+## Development Environment
+
+The project uses **Deno** as the primary development runtime, with cross-runtime support for Node.js and Bun.
+
+### Setup
+```bash
+# Install Deno dependencies
+deno install
+```
+
+## Contribution Guidelines
+
+### Pre-commit Checks
+
+Before committing changes, always run:
+```bash
+deno task pre-commit
+```
+
+This executes:
+- **Formatting check**: `deno fmt --check` - ensures code follows style guidelines
+- **Linting**: `deno lint` - checks for code quality issues
+- **Type checking**: `deno check src/croner.ts` - validates TypeScript types
+
+### Testing
+
+Run tests during development:
+```bash
+deno task test
+```
+
+### Full Build
+
+Before submitting a PR, run the full build to ensure all checks pass:
+```bash
+deno task build
+```
+
+This runs all tests, builds distribution files, and validates the entire codebase.
+
+### Key Points
+
+- Base work on the `dev` branch
+- Add test cases for all changes
+- Zero dependencies - do not add external dependencies
+- Follow existing code style and patterns
+- Update documentation if changing public APIs
+
+For detailed contribution guidelines, see [docs/src/contributing.md](docs/src/contributing.md).