fix: D3FEND ontology-based import, template management UX, and branding

- Rewrite D3FEND import to use tactic-level APIs for reliable technique
  fetching with proper ontology IRIs, descriptions, and tactic assignments
- Fix D3FEND technique URLs to use canonical IRI (no more 404s)
- All 255 D3FEND techniques now have descriptions from the official API
- Change Deactivate button color to red in template management table
- Add custom Aegis logo and favicon replacing default Vite assets
- Remove unused old API parsing code and clean up fallback list

backend/app/schemas/test_template.py

@@ -63,6 +63,7 @@ class TestTemplateSummary(BaseModel):
     source: str
     platform: str | None = None
     severity: str | None = None
+    is_active: bool = True
 
     model_config = ConfigDict(from_attributes=True)