feat: add workflow help metadata, artifact optional flag, and search/filter improvements

- Add WorkflowHelp struct with Usage and ExampleTargets for CLI documentation
- Add Optional field to Artifact model and database schema with migration support
- Implement workflow search functionality by name, description, and tags in CLI list command
- Add --usage and --search flags to workflow list command with multiple filtering options
- Display workflow usage info in show command when Help is defined
- Support help inheritance in workflow extends/inheritance resolver
- Update vulnerability counters from database after SARIF imports
- Add comprehensive Help unit tests covering parsing, cloning, and mutation isolation
- Improve test helpers with streaming output, diagnostics, and file validation utilities
- Add fourth general canary test for domain-list-recon flow with artifact validation

test/testdata/workflows/test-example-report.yaml

@@ -2,6 +2,9 @@ name: test-example-report
 kind: module
 description: Test example report with nested parallel steps with mixed types
 tags: test,parallel,nested
+help:
+  example_targets: ['example.com', 'httpbin.org']
+  usage: osmedeus run -m test-example-report -t <target>
 
 params:
   - name: target
@@ -17,6 +20,7 @@ reports:
     path: "{{Output}}/http.json"
     type: json
     description: Structured JSON output
+    optional: true
 
   - name: markdown-report-report
     path: "{{Output}}/reports/sample-markdown-report.md"