feat: add default explore scope setting

Add user setting to control default visibility scope in /explore page.

Changes:
- Add defaultExploreScopeNostrverse/Friends/Mine to UserSettings type
- Add "Default Explore Scope" setting in ReadingDisplaySettings UI
- Update Explore component to use defaultExploreScope settings
- Set default to friends-only (nostrverse: false, friends: true, mine: false)

Users can now configure which content types (nostrverse/friends/mine)
are visible by default when visiting the explore page, separate from
the highlight visibility settings.

src/components/Explore.tsx

@@ -47,11 +47,11 @@ const Explore: React.FC<ExploreProps> = ({ relayPool, eventStore, settings, acti
   const [myHighlights, setMyHighlights] = useState<Highlight[]>([])
   const [myHighlightsLoading, setMyHighlightsLoading] = useState(false)
   
-  // Visibility filters (defaults from settings, or friends only)
+  // Visibility filters (defaults from settings)
   const [visibility, setVisibility] = useState<HighlightVisibility>({
-    nostrverse: settings?.defaultHighlightVisibilityNostrverse ?? false,
-    friends: settings?.defaultHighlightVisibilityFriends ?? true,
-    mine: settings?.defaultHighlightVisibilityMine ?? false
+    nostrverse: settings?.defaultExploreScopeNostrverse ?? false,
+    friends: settings?.defaultExploreScopeFriends ?? true,
+    mine: settings?.defaultExploreScopeMine ?? false
   })
 
   // Subscribe to highlights controller

src/components/Settings.tsx

@@ -29,6 +29,9 @@ const DEFAULT_SETTINGS: UserSettings = {
   defaultHighlightVisibilityNostrverse: true,
   defaultHighlightVisibilityFriends: true,
   defaultHighlightVisibilityMine: true,
+  defaultExploreScopeNostrverse: false,
+  defaultExploreScopeFriends: true,
+  defaultExploreScopeMine: false,
   zapSplitHighlighterWeight: 50,
   zapSplitBorisWeight: 2.1,
   zapSplitAuthorWeight: 50,

src/components/Settings/ReadingDisplaySettings.tsx

@@ -98,6 +98,45 @@ const ReadingDisplaySettings: React.FC<ReadingDisplaySettingsProps> = ({ setting
         </div>
       </div>
 
+      <div className="setting-group setting-inline">
+        <label>Default Explore Scope</label>
+        <div className="highlight-level-toggles">
+          <IconButton
+            icon={faNetworkWired}
+            onClick={() => onUpdate({ defaultExploreScopeNostrverse: !(settings.defaultExploreScopeNostrverse !== false) })}
+            title="Nostrverse content"
+            ariaLabel="Toggle nostrverse content by default in explore"
+            variant="ghost"
+            style={{ 
+              color: (settings.defaultExploreScopeNostrverse !== false) ? 'var(--highlight-color-nostrverse, #9333ea)' : undefined,
+              opacity: (settings.defaultExploreScopeNostrverse !== false) ? 1 : 0.4
+            }}
+          />
+          <IconButton
+            icon={faUserGroup}
+            onClick={() => onUpdate({ defaultExploreScopeFriends: !(settings.defaultExploreScopeFriends !== false) })}
+            title="Friends content"
+            ariaLabel="Toggle friends content by default in explore"
+            variant="ghost"
+            style={{ 
+              color: (settings.defaultExploreScopeFriends !== false) ? 'var(--highlight-color-friends, #f97316)' : undefined,
+              opacity: (settings.defaultExploreScopeFriends !== false) ? 1 : 0.4
+            }}
+          />
+          <IconButton
+            icon={faUser}
+            onClick={() => onUpdate({ defaultExploreScopeMine: !(settings.defaultExploreScopeMine !== false) })}
+            title="My content"
+            ariaLabel="Toggle my content by default in explore"
+            variant="ghost"
+            style={{ 
+              color: (settings.defaultExploreScopeMine !== false) ? 'var(--highlight-color-mine, #eab308)' : undefined,
+              opacity: (settings.defaultExploreScopeMine !== false) ? 1 : 0.4
+            }}
+          />
+        </div>
+      </div>
+
       <div className="setting-group setting-inline">
         <label htmlFor="readingFont">Reading Font</label>
         <div className="setting-control">

src/services/settingsService.ts

@@ -36,6 +36,10 @@ export interface UserSettings {
   defaultHighlightVisibilityNostrverse?: boolean
   defaultHighlightVisibilityFriends?: boolean
   defaultHighlightVisibilityMine?: boolean
+  // Default explore scope
+  defaultExploreScopeNostrverse?: boolean
+  defaultExploreScopeFriends?: boolean
+  defaultExploreScopeMine?: boolean
   // Zap split weights (treated as relative weights, not strict percentages)
   zapSplitHighlighterWeight?: number // default 50
   zapSplitBorisWeight?: number // default 2.1