feat(app): add nostr social embeds with bech32 NIP-19 decoding

Create NostrEmbed.vue component that renders nostr:note1, nostr:npub1,
and nostr:nevent1 URIs as rich embedded cards. Add bech32 decoder
utility with NIP-19 TLV support for nevent/nprofile. Extend useNostr
with fetchNote() for single-note relay lookups. ChatMessage.vue now
detects and strips nostr URIs, rendering them as inline embed cards.

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

packages/app/src/components/chat/ChatMessage.vue

@@ -75,6 +75,14 @@
         />
       </div>
 
+      <div v-if="nostrUris.length > 0" class="mt-3 space-y-1.5" @click.stop>
+        <NostrEmbed
+          v-for="uri in nostrUris"
+          :key="uri"
+          :uri="uri"
+        />
+      </div>
+
       <div v-if="inlineNewsLinks.length > 0" class="mt-3 space-y-1" @click.stop>
         <NewsCard
           v-for="(link, i) in inlineNewsLinks"
@@ -186,6 +194,7 @@ import SongCard from '@/components/content/SongCard.vue'
 import PodcastCard from '@/components/content/PodcastCard.vue'
 import PlaceCard from '@/components/content/PlaceCard.vue'
 import NewsCard from '@/components/content/NewsCard.vue'
+import NostrEmbed from '@/components/chat/NostrEmbed.vue'
 
 const props = withDefaults(
   defineProps<{
@@ -224,6 +233,13 @@ const inlineNewsLinks = computed(() => inlineContent.value.newsLinks ?? [])
 const inlineWebsitesLinks = computed(() => inlineContent.value.websitesLinks ?? [])
 const inlineMagazineSections = computed(() => inlineContent.value.magazineSections ?? [])
 
+const NOSTR_URI_RE = /nostr:(note1[a-z0-9]{58}|npub1[a-z0-9]{58}|nevent1[a-z0-9]+|nprofile1[a-z0-9]+)/g
+const nostrUris = computed(() => {
+  if (isUser.value) return []
+  const matches = props.message.content.match(NOSTR_URI_RE)
+  return matches ? [...new Set(matches)] : []
+})
+
 const isCodeResponse = computed(() =>
   !isUser.value && props.triggeringQuery.trim().toLowerCase() === '/code'
 )
@@ -261,6 +277,7 @@ const displayText = computed(() => {
   if (isUser.value) return props.message.content
   let text = stripContentTags(props.message.content)
   if (inlineNewsLinks.value.length > 0 || inlineWebsitesLinks.value.length > 0) text = stripMarkdownLinks(text)
+  if (nostrUris.value.length > 0) text = text.replace(NOSTR_URI_RE, '').replace(/\n{3,}/g, '\n\n').trim()
   return text
 })