feat: add aturi.to as share option

Add aturi.to universal link sharing to post share menu, allowing users
to share content that recipients can view on any ATProto client.

Changes:
- Add toShareUrlAturi() function to convert witchsky URLs to aturi.to format
- Implement onSharePostAturi() and onCopyLinkAturi() handlers with analytics
- Add "Share via aturi.to..." and "Copy aturi.to link" menu items

aturi.to links let recipients choose their preferred client (Bluesky,
Blacksky, Anisota, etc.) instead of forcing them to a specific platform.

src/components/PostControls/ShareMenu/ShareMenuItems.tsx

···
 import {makeProfileLink} from '#/lib/routes/links'
 import {type NavigationProp} from '#/lib/routes/types'
 import {shareText, shareUrl} from '#/lib/sharing'
-import {toShareUrl, toShareUrlBsky} from '#/lib/strings/url-helpers'
+import {toShareUrl, toShareUrlBsky, toShareUrlAturi} from '#/lib/strings/url-helpers'
 import {logger} from '#/logger'
 import {isIOS} from '#/platform/detection'
 import {useProfileShadow} from '#/state/cache/profile-shadow'
···
   const onCopyLinkBsky = async () => {
     logger.metric('share:press:copyLink', {}, {statsig: true})
     const url = toShareUrlBsky(href)
+    if (isIOS) {
+      // iOS only
+      await ExpoClipboard.setUrlAsync(url)
+    } else {
+      await ExpoClipboard.setStringAsync(url)
+    }
+    Toast.show(_(msg`Copied to clipboard`), 'clipboard-check')
+    onShareProp()
+  }
+
+  const onSharePostAturi = () => {
+    logger.metric('share:press:nativeShare', {}, {statsig: true})
+    const url = toShareUrlAturi(href)
+    shareUrl(url)
+    onShareProp()
+  }
+
+  const onCopyLinkAturi = async () => {
+    logger.metric('share:press:copyLink', {}, {statsig: true})
+    const url = toShareUrlAturi(href)
     if (isIOS) {
       // iOS only
       await ExpoClipboard.setUrlAsync(url)
···
             onPress={onCopyLinkBsky}>
             <Menu.ItemText>
               <Trans>Copy via bsky.app</Trans>
+            </Menu.ItemText>
+            <Menu.ItemIcon icon={ChainLinkIcon} position="right" />
+          </Menu.Item>
+
+          <Menu.Item
+            testID="postDropdownShareAturiBtn"
+            label={_(msg`Share via aturi.to...`)}
+            onPress={onSharePostAturi}>
+            <Menu.ItemText>
+              <Trans>Share via aturi.to...</Trans>
+            </Menu.ItemText>
+            <Menu.ItemIcon icon={ArrowOutOfBoxIcon} position="right" />
+          </Menu.Item>
+
+          <Menu.Item
+            testID="postDropdownCopyAturiBtn"
+            label={_(msg`Copy aturi.to link`)}
+            onPress={onCopyLinkAturi}>
+            <Menu.ItemText>
+              <Trans>Copy aturi.to link</Trans>
             </Menu.ItemText>
             <Menu.ItemIcon icon={ChainLinkIcon} position="right" />
           </Menu.Item>

src/lib/strings/url-helpers.ts

···
   return url
 }
 
+export function toShareUrlAturi(url: string): string {
+  // Convert witchsky URL to aturi.to format
+  // Expected input format: /profile/handle/post/rkey
+  try {
+    if (!url.startsWith('https')) {
+      const urlp = new URL('https://witchsky.app')
+      urlp.pathname = url
+      url = urlp.toString()
+    }
+
+    const urlp = new URL(url)
+    const pathname = urlp.pathname
+
+    // Extract components from /profile/identifier/post/rkey
+    if (pathname.startsWith('/profile/')) {
+      const parts = pathname.substring(9).split('/') // Remove "/profile/"
+
+      if (parts.length === 3 && parts[1] === 'post') {
+        // Post: /profile/identifier/post/rkey
+        const identifier = parts[0]
+        const rkey = parts[2]
+        return `https://aturi.to/${identifier}/app.bsky.feed.post/${rkey}`
+      } else if (parts.length === 3 && parts[1] === 'lists') {
+        // List: /profile/identifier/lists/rkey
+        const identifier = parts[0]
+        const rkey = parts[2]
+        return `https://aturi.to/${identifier}/app.bsky.graph.list/${rkey}`
+      } else if (parts.length === 1) {
+        // Profile only: /profile/identifier
+        return `https://aturi.to/${parts[0]}`
+      }
+    }
+
+    // Fallback to original URL if we can't parse it
+    return url
+  } catch (e) {
+    console.error('Error converting to aturi.to URL:', e)
+    return url
+  }
+}
+
 export function toBskyAppUrl(url: string): string {
   return new URL(url, BSKY_APP_HOST).toString()
 }