fix: v0.10.1 usage ping uses tab presence; CI-safe test

The usage ping now treats "away" like the needs-you notifier: no DevDesk
tab in view for ~2 minutes. The test sets a presence marker instead of
attaching a tmux client, which never attached in CI. 0.10.0 was never
published.

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

tests/attach.bats

@@ -1173,12 +1173,11 @@ JSONL
     sleep 0.5
     [ "$(posts)" -eq 1 ]
     [[ "$(jq -r .text "$TMP/posts")" == *"91% of the 5-hour window"* ]]
-    # next window, but a client is attached: no post, and that window is done
-    tmux -S "$DEVDESK_SOCKET" new-session -d -s watcher 'sleep 30'
-    script -qc "tmux -S '$DEVDESK_SOCKET' attach -t =alpha" /dev/null </dev/null >/dev/null 2>&1 &
-    for _ in $(seq 1 30); do [ -n "$(tmux -S "$DEVDESK_SOCKET" list-clients -F x)" ] && break; sleep 0.1; done
+    # next window, but a DevDesk tab is in view: no post, and that window is done
+    mkdir -p "$DEVDESK_PRESENCE_DIR" && touch "$DEVDESK_PRESENCE_DIR/1"
     sl 95 2000018000
-    sleep 1
+    for _ in $(seq 1 30); do [ "$(cat "$DEVDESK_STATE_DIR/usage-warned")" = 2000018000 ] && break; sleep 0.1; done
+    sleep 0.5
     [ "$(posts)" -eq 1 ]
     [ "$(cat "$DEVDESK_STATE_DIR/usage-warned")" = 2000018000 ]
 }