test: add unit tests for MarkdownEditorComponent

[corvid-agent]

Summary

MarkdownEditorComponent has a spec.md (added in #68) but no unit test file. The component wraps CodeMirror 6 with non-trivial lifecycle management including a suppressUpdate feedback-loop prevention mechanism that should be verified.

Recommended test cases

Scenario	Description
Initial render	Component creates, CodeMirror EditorView is instantiated
Content change emission	User typing emits contentChange with full document text
External content sync	Changing the content input dispatches a transaction to update the editor
Identical content no-op	Setting same content value does not dispatch a transaction
Suppress flag	After user edit, the next effect run skips dispatch (prevents feedback loop)
Destroy cleanup	ngOnDestroy calls view.destroy()

Notes

• CodeMirror requires a DOM host element; tests will need careful setup with jsdom
• May need to spy on EditorView constructor and dispatch method
• Consider whether fake-indexeddb (already in devDependencies) is relevant here

Files

• Source: src/app/components/markdown-editor/markdown-editor.ts
• Spec: specs/components/markdown-editor.spec.md
• Test (to create): src/app/components/markdown-editor/markdown-editor.spec.ts