workstation: tmux sessions survive devvm reboots (save timer + boot restore)

Viktor: emo's open web-terminal sessions must persist across reboots.
Claude conversations were already durable on disk; the volatile part
was the tmux wiring (which named session runs which conversation).

t3-tmux-sessions save (5-min timer) snapshots every roster user's
sessions to /var/lib/t3-tmux-state/<user>.tsv — conversation uuid
taken from argv --resume (self-sustaining once restored) or the
newest transcript in the cwd-slug project dir created after process
start (fresh launcher sessions; claude does NOT hold its transcript
fd open, so fd-sniffing was a dead end). t3-tmux-sessions restore
(boot oneshot, also safe after partial loss) recreates missing
sessions with claude --resume <uuid>. Reconciler self-heals both
units' enablement.

Verified live: emo's 5 sessions snapshotted with correct uuids;
killed R730-cooling -> restore brought it back resuming the same
conversation (context meter identical); other sessions untouched.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/t3-tmux-save.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=Periodic workstation tmux session snapshot
+
+[Timer]
+OnBootSec=10min
+OnCalendar=*:0/5
+Persistent=false
+
+[Install]
+WantedBy=timers.target