fix: apply block/mute list filtering to DM messages and conversations

The user's block/mute list (NIP-51) was not being checked when
processing direct messages, allowing blocked users' messages to appear
in conversations, trigger notifications, and increment unseen counts.

This adds block filtering at four layers:
- nostrService.applyDirectMessage: drops incoming DMs from blocked users
  before they enter the in-memory message cache
- nostrService.persistDirectMessageRecord: prevents blocked DM senders
  from being persisted to IndexedDB or triggering notifications
- profileModalController.buildDmConversationData: filters blocked users
  from the conversation list UI (catches pre-block persisted messages)
- applicationBootstrap: excludes blocked-user conversations from the
  unread DM badge count

The block checker is injected via setDmBlockChecker() to keep
nostrService decoupled from userBlocks, wired up in app.js init().

https://claude.ai/code/session_01EAVLtAM14GN99Eik8otLg2

js/app.js

@@ -628,6 +628,15 @@ class Application {
       this.authService.hydrateFromStorage();
       this.renderSavedProfiles();
 
+      if (
+        this.nostrService &&
+        typeof this.nostrService.setDmBlockChecker === "function"
+      ) {
+        this.nostrService.setDmBlockChecker((pubkey) =>
+          this.isAuthorBlocked(pubkey),
+        );
+      }
+
       loadModerationOverridesFromStorage();
       loadModerationSettingsFromStorage();
       loadDmPrivacySettingsFromStorage();