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>

bin/devdesk

@@ -141,11 +141,17 @@ cmd_rename() {
     if dd_server_up && dd_tmux has-session -t "=$old" 2>/dev/null; then running=1; fi
     [ "$running" = 1 ] || [ -n "$(dd_registry_get "$old" dir)" ] || dd_die "no session named '$old'"
     ! session_exists "$new" || dd_die "a session named '$new' already exists"
-    if [ "$running" = 1 ]; then
-        dd_tmux rename-session -t "=$old" "$new"
-        dd_tmux set-environment -t "=$new" DEVDESK_SESSION "$new"
+    dd_registry_locked rename_locked "$old" "$new" "$running" || dd_die "could not rename '$old'"
+}
+
+# tmux and the registry change together, under the registry lock (see
+# devdesk-session-hook).
+rename_locked() {
+    if [ "$3" = 1 ]; then
+        dd_tmux rename-session -t "=$1" "$2" || return 1
+        dd_tmux set-environment -t "=$2" DEVDESK_SESSION "$2"
     fi
-    dd_registry_rename "$old" "$new"
+    dd_registry_rename "$1" "$2"
 }
 
 cmd_end() {