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>

etc/env

@@ -1,8 +1,9 @@
 # DevDesk defaults, shipped by the package. Don't edit: put your changes in
 # /etc/devdesk/env.local (same KEY=value format, read after this file), so
 # package upgrades never prompt about this file.
-# Read by systemd (EnvironmentFile=) and by the devdesk scripts. Plain KEY=value
-# lines only: systemd does not support inline comments.
+# Read by systemd (EnvironmentFile=) and by the devdesk scripts, the same way:
+# plain KEY=value lines, values taken literally (no $VAR, no $(…)), optionally
+# in quotes. No inline comments. Other lines are ignored with a warning.
 # The ttyd credential lives in /etc/devdesk/secret.env (generated on install).
 
 # Port ttyd listens on (NPM proxies dev.lotusguild.org here).