feat(phase-15): add Test Catalog page, template instantiation, and auto-migration entrypoint (T-119, T-120, T-121)

T-119: TestCatalogPage with search, filters (source/platform/severity), template cards grid, and pagination

T-120: TestFromTemplateForm modal with pre-filled fields from template, required field validation, and redirect on creation

T-121: Integrate Available Test Templates section in TechniqueDetailPage with Run This Test buttons; fix missing testStateBadgeColors for new states

Also: add backend entrypoint.sh for automatic Alembic migrations + seed on container startup, add curl to Dockerfile for healthcheck

frontend/src/components/Sidebar.tsx

@@ -3,6 +3,7 @@ import {
   LayoutDashboard,
   Shield,
   FlaskConical,
+  BookOpen,
   Settings,
   Users,
   FileText,
@@ -13,6 +14,7 @@ const baseLinks = [
   { to: "/dashboard", label: "Dashboard", icon: LayoutDashboard },
   { to: "/techniques", label: "Techniques", icon: Shield },
   { to: "/tests", label: "Tests", icon: FlaskConical },
+  { to: "/test-catalog", label: "Test Catalog", icon: BookOpen },
 ];
 
 const adminLinks = [