feat: v0.12.0 Settings window, per-session Remote Control, delete conversations

- Settings (⋯ → Settings…, palette): theme, terminal text size, interface
  size, notifications, Remote Control & privacy. The ⋯ menu shrinks.
- Remote Control per session: registry choice > Settings default >
  DEVDESK_REMOTE_CONTROL. Switching an idle session restarts its Claude
  on the same conversation; busy sessions change at the next start.
  rc_active comes from the running process; RC tag on sessions.
- --delete-convo: remove a conversation's local transcript and subagent
  files; refused while in use. Delete… in Search past conversations.
Closes #61

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHRLCCdXYm41Qx5kNhehaP

etc/env

@@ -62,5 +62,7 @@ DEVDESK_USAGE_WARN=90
 # /etc/devdesk/guard.local, one "regex<TAB>reason" per line.
 DEVDESK_GUARD=1
 
-# 1 = also enable Remote Control so sessions can be continued from the Claude app.
+# Remote Control default for new sessions (1 = on: continue them from the Claude app;
+# Anthropic then stores the transcript to sync devices). Settings in the web UI
+# overrides this, and each session can choose its own (devdesk#61).
 DEVDESK_REMOTE_CONTROL=0