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

frontend/src/components/Sidebar.tsx

@@ -2,7 +2,6 @@ import { NavLink } from "react-router-dom";
 import { useState } from "react";
 import {
   LayoutDashboard,
-  Shield,
   FlaskConical,
   BookOpen,
   BarChart3,
@@ -132,8 +131,8 @@ export default function Sidebar() {
   return (
     <aside className="flex h-screen w-60 flex-col border-r border-gray-800 bg-gray-900">
       {/* Logo */}
-      <div className="flex h-16 items-center gap-2 px-5">
-        <Shield className="h-7 w-7 text-cyan-400" />
+      <div className="flex h-16 items-center gap-3 px-5">
+        <img src="/aegis-logo.svg" alt="Aegis" className="h-8 w-8" />
         <span className="text-lg font-bold tracking-wide text-white">
           Aegis
         </span>