Comments on plays

- Anyone who can see a play can read its comments; the player and the people they follow can write.
  The author, the player and admins can delete; comments can be reported (admins see the text).
- Notifications: "commented on" for the player, "replied on" for earlier commenters, each with its
  own setting. Reaction and comment notifications now open the play.
- A 💬 chip with the count next to reactions on the feed and recent plays, opening the thread on
  the app (/play/[id]) and the website. Threads refresh every few seconds while open.
- Blocking removes comments between the two people. Plays with comments survive history trimming.
- Privacy page updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011Y2iUsKEWDuRGjK5FPmcUP

apps/mobile/src/app/_layout.tsx

@@ -109,6 +109,7 @@ function AppNavigator() {
           <Stack.Screen name="scan" options={{ title: 'Scan a code', presentation: 'modal' }} />
           <Stack.Screen name="notifications" options={{ title: 'Notifications' }} />
           <Stack.Screen name="t/[id]" options={{ title: '' }} />
+          <Stack.Screen name="play/[id]" options={{ title: 'Comments' }} />
           <Stack.Screen name="send/[trackId]" options={{ title: 'Send to friends', presentation: 'modal' }} />
         </Stack.Protected>
         <Stack.Protected guard={!signedIn}>