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/pages/LoginPage.tsx

@@ -1,6 +1,5 @@
 import { useState, type FormEvent } from "react";
 import { useNavigate } from "react-router-dom";
-import { Shield } from "lucide-react";
 import { useAuth } from "../context/AuthContext";
 
 export default function LoginPage() {
@@ -37,8 +36,8 @@ export default function LoginPage() {
     <div className="flex min-h-screen items-center justify-center bg-gray-950 px-4">
       <div className="w-full max-w-sm space-y-8">
         {/* Logo */}
-        <div className="flex flex-col items-center gap-2">
-          <Shield className="h-12 w-12 text-cyan-400" />
+        <div className="flex flex-col items-center gap-3">
+          <img src="/aegis-logo.svg" alt="Aegis" className="h-16 w-16" />
           <h1 className="text-2xl font-bold tracking-wide text-white">
             Aegis
           </h1>