Development environment setup (#122)

Create `AGENTS.md` to document development environment setup and
production testing workflow.

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Mason Williams <masnwilliams@users.noreply.github.com>

Author: masnwilliams

AGENTS.md

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+# Kernel CLI
+
+## Cursor Cloud specific instructions
+
+This is a Go CLI application (no long-running services). Development commands are in the `Makefile`:
+
+- **Build:** `make build` → produces `./bin/kernel`
+- **Test:** `make test` → runs `go vet` + `go test ./...`
+- **Lint:** `make lint` → runs `golangci-lint run` (requires `golangci-lint` on `PATH`)
+
+### Testing against production
+
+When `KERNEL_API_KEY` is set (provided as a secret), the CLI hits the **production** Kernel API. After `make build`, test with `./bin/kernel`. Useful smoke-test sequence:
+
+1. `./bin/kernel auth status` — verify auth
+2. `./bin/kernel app list` — list deployed apps
+3. `./bin/kernel browsers create` — create a browser session (remember to delete it after)
+4. `./bin/kernel browsers delete <session_id>` — clean up
+
+Be mindful that these operations affect production resources.
+
+### Gotchas
+
+- `golangci-lint` is installed via `go install` to `$(go env GOPATH)/bin`. This directory must be on `PATH` (the update script handles this via `.bashrc`).
+- The Makefile's `lint` target uses `|| true`, so it always exits 0 even when lint issues exist. Pre-existing lint warnings (errcheck, staticcheck) are present in the codebase and expected.
+- The `go-keyring` dependency requires D-Bus and `libsecret` on Linux. These are pre-installed in the Cloud VM.
+- `kernel create` works locally without authentication. Most other commands (`deploy`, `invoke`, `browsers`, etc.) require a `KERNEL_API_KEY` env var or `kernel login` OAuth flow.
+- Go module path is `github.com/kernel/cli`. The project requires Go 1.25.0 (specified in `go.mod`).