rename(cleanup): drop last capakraken strings from UI, scripts, schema, tests

AppShell.tsx top-left brand → Nexus (desktop sidebar + mobile top-bar),
shell echo strings, prisma schema header, test fixture token, playwright
runtime DB URL.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/start.sh

@@ -5,7 +5,7 @@ cd "$(dirname "$0")/.."
 APP_PORT="${APP_PORT:-3100}"
 APP_CONTAINER="${APP_CONTAINER:-$(docker compose --profile full ps -q app 2>/dev/null | head -1)}"
 
-echo "Starting CapaKraken..."
+echo "Starting Nexus..."
 
 # 1. Start Docker services
 echo "  Starting PostgreSQL + Redis..."
@@ -34,7 +34,7 @@ echo "  Waiting for server (up to 90s)..."
 for i in {1..90}; do
   if curl -sf "http://localhost:${APP_PORT}/api/health" > /dev/null 2>&1; then
     echo ""
-    echo "CapaKraken is running!"
+    echo "Nexus is running!"
     curl -s "http://localhost:${APP_PORT}/api/ready" | python3 -m json.tool 2>/dev/null || curl -s "http://localhost:${APP_PORT}/api/ready"
     echo ""
     echo "  URL: http://localhost:${APP_PORT}"