semi implemented and features implemented save checkpoint

docs/features/unchecked/web/sbom-diff-side-by-side-panel.md

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+# SBOM Diff Side-by-Side Panel
+
+## Module
+Web
+
+## Status
+IMPLEMENTED
+
+## Description
+Side-by-side visual comparison panel showing packages added/removed/changed between two SBOM versions, with highlighted risk changes for before/after risk state comparison.
+
+## Implementation Details
+- **Feature directory**: `src/Web/StellaOps.Web/src/app/features/sbom-diff/`
+- **Routes**: `sbom-diff.routes.ts`
+- **Components**:
+  - `sbom-diff-view` (`src/Web/StellaOps.Web/src/app/features/sbom-diff/components/sbom-diff-view/sbom-diff-view.component.ts`)
+- **Services**:
+  - `sbom-diff` (`src/Web/StellaOps.Web/src/app/features/sbom-diff/services/sbom-diff.service.ts`)
+- **Models**:
+  - `src/Web/StellaOps.Web/src/app/features/sbom-diff/models/sbom-diff.models.ts`
+- **Source**: SPRINT_20251226_004_FE_risk_dashboard.md
+
+## E2E Test Plan
+- **Setup**:
+  - [ ] Log in with a user that has appropriate permissions
+  - [ ] Navigate to `/sbom/diff`
+  - [ ] Ensure test data exists (scanned artifacts, SBOM data, or seed data as needed)
+- **Core verification**:
+  - [ ] Verify the panel/drawer opens on trigger (click, keyboard shortcut)
+  - [ ] Verify the panel displays the correct detail data for the selected item
+  - [ ] Verify the panel can be closed (X button, Escape key, backdrop click)
+- **Edge cases**:
+  - [ ] Verify graceful handling when backend API is unavailable (error state)
+  - [ ] Verify responsive layout at different viewport sizes
+  - [ ] Verify accessibility (keyboard navigation, screen reader labels, ARIA attributes)