fix: v0.9.1 robustness cleanups

- run_resume falls back to a new conversation only when the transcript file
  is gone; other failures end at the menu with the recorded id intact.
- The SessionStart hook resolves the session name under the registry lock;
  rename holds it across tmux rename-session and the registry move
  (dd_registry_locked, nestable).
- dd_load_env parses KEY=value like systemd instead of sourcing the files.
- devdesk-deploy: DPkg::Lock::Timeout, explicit FAILED lines on stdout and in
  the log; the hook answers synchronously and CI checks the HTTP status.
  logrotate for the deploy log.
- postinst drops duplicate terminal-features entries; hooks sweep stale
  temp files.

Closes #12

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

debian/devdesk.postinst

@@ -13,6 +13,13 @@ configure)
     # Apply tmux.conf changes to a running server without restarting it.
     if [ -S /run/devdesk/tmux.sock ]; then
         tmux -N -S /run/devdesk/tmux.sock source-file /usr/share/devdesk/tmux.conf >/dev/null 2>&1 || true
+        # Before 0.3.1 every upgrade appended another copy of DevDesk's
+        # terminal-features entry; tmux.conf now sets index 90. Drop the copies.
+        tmux -N -S /run/devdesk/tmux.sock show -s terminal-features 2>/dev/null |
+            awk '$2 == "xterm-256color:RGB" && $1 != "terminal-features[90]" { print $1 }' |
+            while read -r opt; do
+                tmux -N -S /run/devdesk/tmux.sock set -su "$opt" >/dev/null 2>&1 || true
+            done
     fi
     ;;
 esac