Wire up NIP-19 / NIP-21 navigation + hashtag search from notes

- Mention clicks (nostr:npub1, nostr:nprofile) open internal ProfileView
- njump.me links intercepted: npub/nprofile decoded and opened internally,
  note/nevent/naddr fall through to browser (no reader yet)
- Hashtag clicks navigate to SearchView and auto-run the search
- openSearch(query) action added to UIStore; pendingSearch consumed on mount

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

src/stores/ui.ts

@@ -10,9 +10,11 @@ interface UIState {
   selectedPubkey: string | null;
   selectedNote: NDKEvent | null;
   previousView: View;
+  pendingSearch: string | null;
   setView: (view: View) => void;
   openProfile: (pubkey: string) => void;
   openThread: (note: NDKEvent, from: View) => void;
+  openSearch: (query: string) => void;
   goBack: () => void;
   toggleSidebar: () => void;
 }
@@ -23,9 +25,11 @@ export const useUIStore = create<UIState>((set, _get) => ({
   selectedPubkey: null,
   selectedNote: null,
   previousView: "feed",
+  pendingSearch: null,
   setView: (currentView) => set({ currentView }),
   openProfile: (pubkey) => set((s) => ({ currentView: "profile", selectedPubkey: pubkey, previousView: s.currentView as View })),
   openThread: (note, from) => set({ currentView: "thread", selectedNote: note, previousView: from }),
+  openSearch: (query) => set({ currentView: "search", pendingSearch: query }),
   goBack: () => set((s) => ({
     currentView: s.previousView !== s.currentView ? s.previousView : "feed",
     selectedNote: null,