semi implemented and features implemented save checkpoint

docs/features/unchecked/cli/cli-api-spec-download-command.md

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+# CLI API Spec Download Command
+
+## Module
+Cli
+
+## Status
+IMPLEMENTED
+
+## Description
+`stella api spec download` command for retrieving the aggregate OpenAPI specification with checksum/ETag verification, enabling offline API reference consumption.
+
+## Implementation Details
+- **Command Handlers**: `src/Cli/StellaOps.Cli/Commands/CommandHandlers.cs` -- partial class containing API spec download handler
+- **Command Registration**: `src/Cli/StellaOps.Cli/Commands/CommandFactory.cs` -- registers `api spec download` in command tree
+- **Sprint**: SPRINT_0204_0001_0004_cli_iv
+- **Commands**:
+  - `stella api spec download` -- download the aggregate OpenAPI spec. Options: `--output <path>`, `--format json|yaml`, `--verify` (checksum/ETag verification)
+
+## E2E Test Plan
+- [ ] Run `stella api spec download --output ./openapi.json` and verify OpenAPI spec file created
+- [ ] Run `stella api spec download --format yaml` and verify YAML format output
+- [ ] Run `stella api spec download --verify` and verify checksum/ETag verification passes
+- [ ] Run command again and verify ETag caching skips re-download when spec unchanged
+- [ ] Verify downloaded spec is valid OpenAPI 3.x format
+- [ ] Verify error handling when API server is unreachable