chore: add AGENTS.md and CLAUDE.md

AGENTS.md

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+# Ploy
+
+Terminal-based deployment tool for AWS services. Defines desired service versions in YAML config files and can verify/deploy them.
+
+## Stack
+
+- Go 1.23, modules
+- CLI framework: Cobra
+- AWS SDK v2 (Lambda, ECS, EventBridge)
+- Config format: YAML
+
+## Project Structure
+
+- `cmd/` - CLI commands (deploy, verify, update)
+- `engine/` - Deployment engines (Lambda, ECS, ECS Scheduled Tasks)
+- `deployments/` - Config parsing, deploy/verify/update orchestration
+- `utils/` - Shared helpers
+
+## Development
+
+No Makefile. Use standard Go commands:
+
+```bash
+go build ./...
+go test ./...
+go install .  # install locally
+```
+
+## CI/CD
+
+- **PR**: `go build ./...` (`.github/workflows/pr-build.yml`)
+- **Release**: Tag `v*.*.*` triggers GoReleaser (`.github/workflows/release.yml`). Create releases via GitHub UI. `source-deployments` picks up the latest release automatically.
+
+## Architecture Notes
+
+- Each deployment engine implements the `DeploymentEngine` interface in `engine/core.go` and registers itself via `RegisterDeploymentEngine` in an `init()` function.
+- Config files are per-environment YAML (e.g. `development.yml`, `production.yml`).
+- The `update` command only modifies the YAML file; it does not deploy. Run `deploy` separately.

CLAUDE.md

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+@AGENTS.md