chore(m6): bump HomePage hero + roadmap card to M6

The home page still advertised "M4 milestone (MITRE ATT&CK)" in the hero
and "M5 — Test & scenario templates" as the next milestone on the
roadmap card — so a visitor landing on `/` couldn't tell M5 and M6 had
shipped, even though the Missions nav entry was wired and the M6 routes
were reachable.

Hero now reads "M6 milestone (Missions & snapshot)" and the roadmap card
points at M7 — Red & blue execution as next.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/pages/HomePage.tsx

@@ -61,7 +61,7 @@ export function HomePage() {
           <span className="text-purple">Purple Team Platform</span>
         </h1>
         <p className="font-mono text-sm font-light text-text-dim mt-2">
-          Collaborative red &amp; blue test orchestration — M4 milestone (MITRE ATT&amp;CK)
+          Collaborative red &amp; blue test orchestration — M6 milestone (Missions &amp; snapshot)
         </p>
       </header>
       <SectionHeader
@@ -141,9 +141,9 @@ export function HomePage() {
 
         <Card accent="purple" title="Roadmap" sub="14 milestones">
           <p>
-            M0 + M1 + M2 + M3 + M4 done. Next:{' '}
+            M0 + M1 + M2 + M3 + M4 + M5 + M6 done. Next:{' '}
             <code className="accent-fill-cyan px-2 py-[2px] rounded-sm font-mono text-4xs">
-              M5 — Test &amp; scenario templates
+              M7 — Red &amp; blue execution on a mission test
             </code>
             .
           </p>