fix(KB-083): fix SpecEditor layout with proper CSS and remove hardcoded rows

- Add comprehensive CSS styles for SpecEditor component layout
- Remove hardcoded rows prop from SpecEditor for flexible sizing
- Add layout tests for SpecEditor to verify responsive behavior
- Include changeset for patch release of @dustinbyrne/kb package

.changeset/fix-spec-editor-layout.md

@@ -0,0 +1,11 @@
+---
+"@dustinbyrne/kb": patch
+---
+
+Fix SpecEditor layout to fill available modal space
+
+- Added CSS styles for `.spec-editor` component with flex layout
+- Removed hardcoded `rows={20}` from textarea in favor of CSS-based sizing
+- Toolbar stays fixed at top while content scrolls
+- AI revision section stays at bottom
+- Added responsive styles for mobile viewports