Add scheduled messages and strip markdown from iMessage responses

Strip markdown formatting (bold, italic, headers, code, links, lists) from
LLM responses before sending via iMessage. Add scheduled messages feature
with CRUD API, background scheduler loop, and admin frontend panel.

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

raggr-frontend/src/components/ui/badge.tsx

@@ -9,6 +9,7 @@ const badgeVariants = cva(
         default: "bg-leaf-pale text-leaf-dark border border-leaf-light/50",
         amber: "bg-amber-pale text-amber-glow border border-amber-soft/40",
         muted: "bg-sand-light/60 text-warm-gray border border-sand/40",
+        destructive: "bg-red-50 text-red-600 border border-red-200/50",
       },
     },
     defaultVariants: {