Fix nostr entity matching in paste handler (#197)

* fix: only match nostr entities at word boundaries in paste handler

Updates the paste handler regex to only match nostr bech32 entities
(npub, note, nevent, naddr, nprofile) when surrounded by whitespace or
at string boundaries. This prevents URLs containing nostr entities
(e.g., https://njump.me/npub1...) from being incorrectly converted
to mentions.

Uses a capture group (^|\s) instead of lookbehind assertion for
Safari compatibility (lookbehind only supported in Safari 16.4+).

* fix: disable pointer events on links in editor

Adds pointer-events: none to anchor tags within the ProseMirror editor
to prevent clicking on pasted URLs from navigating away. This allows
users to edit the text containing links rather than accidentally
triggering navigation.

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/index.css

@@ -392,6 +392,11 @@ body.animating-layout
   top: 0;
 }
 
+/* Disable link navigation in editor - allow editing instead of clicking */
+.ProseMirror a {
+  pointer-events: none;
+}
+
 /* Mention styles */
 .ProseMirror .mention {
   color: hsl(var(--primary));