feat: add Web Share Target support for auto-saving shared URLs

- Add share_target to manifest.webmanifest with POST method
- Implement service worker handler for POST /share-target requests
- Create ShareTargetHandler component to process and save shared URLs
- Add /share-target route in App.tsx
- Auto-saves shared URLs as web bookmarks (NIP-B0)
- Handles Android case where url param is omitted from share data

public/manifest.webmanifest

@@ -9,6 +9,16 @@
   "background_color": "#0b1220",
   "orientation": "any",
   "categories": ["productivity", "social", "utilities"],
+  "share_target": {
+    "action": "/share-target",
+    "method": "POST",
+    "enctype": "multipart/form-data",
+    "params": {
+      "title": "title",
+      "text": "text",
+      "url": "link"
+    }
+  },
   "icons": [
     {
       "src": "/icon-192.png",

src/App.tsx

@@ -15,6 +15,7 @@ import Debug from './components/Debug'
 import Bookmarks from './components/Bookmarks'
 import RouteDebug from './components/RouteDebug'
 import Toast from './components/Toast'
+import ShareTargetHandler from './components/ShareTargetHandler'
 import { useToast } from './hooks/useToast'
 import { useOnlineStatus } from './hooks/useOnlineStatus'
 import { RELAYS } from './config/relays'
@@ -159,6 +160,10 @@ function AppRoutes({
 
   return (
     <Routes>
+      <Route 
+        path="/share-target" 
+        element={<ShareTargetHandler relayPool={relayPool} />} 
+      />
       <Route 
         path="/a/:naddr" 
         element={

src/components/ShareTargetHandler.tsx

@@ -0,0 +1,99 @@
+import { useEffect, useState } from 'react'
+import { useNavigate, useLocation } from 'react-router-dom'
+import { FontAwesomeIcon } from '@fortawesome/react-fontawesome'
+import { faSpinner } from '@fortawesome/free-solid-svg-icons'
+import { Hooks } from 'applesauce-react'
+import { RelayPool } from 'applesauce-relay'
+import { createWebBookmark } from '../services/webBookmarkService'
+import { getActiveRelayUrls } from '../services/relayManager'
+import { useToast } from '../hooks/useToast'
+
+interface ShareTargetHandlerProps {
+  relayPool: RelayPool
+}
+
+/**
+ * Handles incoming shared URLs from the Web Share Target API.
+ * Auto-saves the shared URL as a web bookmark (NIP-B0).
+ */
+export default function ShareTargetHandler({ relayPool }: ShareTargetHandlerProps) {
+  const navigate = useNavigate()
+  const location = useLocation()
+  const activeAccount = Hooks.useActiveAccount()
+  const { showToast } = useToast()
+  const [processing, setProcessing] = useState(false)
+  const [waitingForLogin, setWaitingForLogin] = useState(false)
+
+  useEffect(() => {
+    const handleSharedContent = async () => {
+      // Parse query parameters
+      const params = new URLSearchParams(location.search)
+      const link = params.get('link')
+      const title = params.get('title')
+      const text = params.get('text')
+
+      // Validate we have a URL
+      if (!link) {
+        showToast('No URL to save')
+        navigate('/')
+        return
+      }
+
+      // If no active account, wait for login
+      if (!activeAccount) {
+        setWaitingForLogin(true)
+        showToast('Please log in to save this bookmark')
+        return
+      }
+
+      // We have account and URL, proceed with saving
+      if (!processing) {
+        setProcessing(true)
+        try {
+          await createWebBookmark(
+            link,
+            title || undefined,
+            text || undefined,
+            undefined,
+            activeAccount,
+            relayPool,
+            getActiveRelayUrls(relayPool)
+          )
+          showToast('Bookmark saved!')
+          navigate('/me/links')
+        } catch (err) {
+          console.error('Failed to save shared bookmark:', err)
+          showToast('Failed to save bookmark')
+          navigate('/')
+        } finally {
+          setProcessing(false)
+        }
+      }
+    }
+
+    handleSharedContent()
+  }, [activeAccount, location.search, navigate, relayPool, showToast, processing])
+
+  // Show waiting for login state
+  if (waitingForLogin && !activeAccount) {
+    return (
+      <div className="flex items-center justify-center h-screen">
+        <div className="text-center">
+          <FontAwesomeIcon icon={faSpinner} spin className="text-4xl mb-4" />
+          <p className="text-lg">Waiting for login...</p>
+        </div>
+      </div>
+    )
+  }
+
+  // Show processing state
+  return (
+    <div className="flex items-center justify-center h-screen">
+      <div className="text-center">
+        <FontAwesomeIcon icon={faSpinner} spin className="text-4xl mb-4" />
+        <p className="text-lg">Saving bookmark...</p>
+      </div>
+    </div>
+  )
+}
+

src/sw.ts

@@ -98,10 +98,36 @@ sw.addEventListener('message', (event: ExtendableMessageEvent) => {
   }
 })
 
-// Log fetch errors for debugging (doesn't affect functionality)
+// Handle Web Share Target POST requests
 sw.addEventListener('fetch', (event: FetchEvent) => {
   const url = new URL(event.request.url)
   
+  // Handle POST to /share-target (Web Share Target API)
+  if (event.request.method === 'POST' && url.pathname === '/share-target') {
+    event.respondWith((async () => {
+      const formData = await event.request.formData()
+      const title = (formData.get('title') || '').toString()
+      const text = (formData.get('text') || '').toString()
+      let link = (formData.get('link') || '').toString()
+      
+      // Android often omits url param, extract from text
+      if (!link && text) {
+        const urlMatch = text.match(/https?:\/\/[^\s]+/)
+        if (urlMatch) {
+          link = urlMatch[0]
+        }
+      }
+      
+      const queryParams = new URLSearchParams()
+      if (link) queryParams.set('link', link)
+      if (title) queryParams.set('title', title)
+      if (text) queryParams.set('text', text)
+      
+      return Response.redirect(`/share-target?${queryParams.toString()}`, 303)
+    })())
+    return
+  }
+  
   // Don't interfere with WebSocket connections (relay traffic)
   if (url.protocol === 'ws:' || url.protocol === 'wss:') {
     return