feat: add offline highlight creation with local relay tracking

- Add relay tracking to Highlight type (publishedRelays, isLocalOnly fields)
- Create utility functions to identify local relays (localhost/127.0.0.1)
- Update highlight creation service to track which relays received the event
- Detect when highlights are only on local relays and mark accordingly
- Add visual indicator in UI for local-only highlights with amber badge
- Enable immediate display of highlights created offline
- Ensure highlights work even when only local relay is available

src/components/HighlightItem.tsx

@@ -1,6 +1,6 @@
 import React, { useEffect, useRef } from 'react'
 import { FontAwesomeIcon } from '@fortawesome/react-fontawesome'
-import { faQuoteLeft, faExternalLinkAlt } from '@fortawesome/free-solid-svg-icons'
+import { faQuoteLeft, faExternalLinkAlt, faHouseSignal } from '@fortawesome/free-solid-svg-icons'
 import { Highlight } from '../types/highlights'
 import { formatDistanceToNow } from 'date-fns'
 import { useEventModel } from 'applesauce-react/hooks'
@@ -91,6 +91,16 @@ export const HighlightItem: React.FC<HighlightItemProps> = ({ highlight, onSelec
             {formatDistanceToNow(new Date(highlight.created_at * 1000), { addSuffix: true })}
           </span>
           
+          {highlight.isLocalOnly && (
+            <>
+              <span className="highlight-meta-separator">•</span>
+              <span className="highlight-local-indicator" title="This highlight is only stored on your local relay">
+                <FontAwesomeIcon icon={faHouseSignal} />
+                <span className="highlight-local-text">Local</span>
+              </span>
+            </>
+          )}
+          
           {sourceLink && (
             <a
               href={sourceLink}