Add "Public" badge to Spot Chat header + clearer privacy note

Makes it unmistakable that Spot Chat messages are public and unencrypted:
- Amber "🌐 Public" badge next to the title with an explanatory tooltip
- Footer note reworded to point users to Direct Messages for private chats

Co-authored-by: shakespeare.diy <assistant@shakespeare.diy>

src/components/SpotChat.tsx

@@ -2,7 +2,7 @@ import { useEffect, useMemo, useRef, useState } from 'react';
 import { formatDistanceToNowStrict } from 'date-fns';
 import { Link } from 'react-router-dom';
 import { nip19 } from 'nostr-tools';
-import { MessageCircle, Send, Radio, Info } from 'lucide-react';
+import { MessageCircle, Send, Radio, Info, Globe } from 'lucide-react';
 
 import { Avatar, AvatarFallback, AvatarImage } from '@/components/ui/avatar';
 import { Button } from '@/components/ui/button';
@@ -210,6 +210,14 @@ export function SpotChat({
           <CardTitle className="text-lg flex items-center gap-2">
             <MessageCircle className="h-5 w-5 text-orange-500" />
             Spot Chat
+            <Badge
+              variant="outline"
+              className="gap-1 border-amber-500/40 bg-amber-500/10 text-amber-600 dark:text-amber-400 text-[10px] font-bold uppercase tracking-wide"
+              title="Anyone can read messages in this channel — it is public and unencrypted."
+            >
+              <Globe className="h-3 w-3" />
+              Public
+            </Badge>
           </CardTitle>
           <div className="flex items-center gap-2">
             <TrustFilter value={trustLevel} onChange={setTrustLevel} compact />
@@ -294,8 +302,9 @@ export function SpotChat({
                 </Button>
               </form>
               <p className="mt-1.5 flex items-center gap-1 text-[10px] text-muted-foreground">
-                <Info className="h-3 w-3" />
+                <Info className="h-3 w-3 shrink-0" />
-                Public &amp; ephemeral — this is here-and-now chat, not stored forever.
+                Anyone can read this — messages are public &amp; ephemeral. For private
+                chats, use Direct Messages.
               </p>
             </>
           ) : (