feat: v0.5.0 header, switcher, phone key bar, shared polling, Matrix "needs you"

- Header: no SSO chip ("Sign in again" only on expiry), state dot on the
  session chip, LIVE as a dot, ⋯ menu for text size/notifications/fullscreen,
  Panels badge for waiting sessions and alerts.
- Session switcher on the chip; bare URL reattaches the last session; + New
  opens the panel form with project folders.
- Notifications when other sessions start waiting; alerts polled with the
  panels closed; one tab polls for all tabs over BroadcastChannel.
- Sidebar: context bar per session instead of the Context panel; compact
  Repo/CI with "Ask Claude to fix CI"; legible labels.
- Phone: key bar, drawer with backdrop, visualViewport-aware layout, DOM
  renderer on touch, compact connection dot.
- devdesk-notify-matrix: one Matrix message per wait that lasts
  DEVDESK_MATRIX_DELAY seconds with nobody attached.

Closes #8
Closes #13
Closes #14
Closes #15
Closes #16
Closes #17
Closes #28

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

libexec/devdesk-lib.sh

@@ -34,6 +34,9 @@ dd_load_env
 : "${DEVDESK_GRAFANA_PUBLIC_URL:=$DEVDESK_GRAFANA_URL}"
 : "${DEVDESK_GRAFANA_TOKEN_FILE:=/etc/devdesk/grafana-token}"
 : "${DEVDESK_UPLOAD_MAX:=26214400}"
+: "${DEVDESK_PUBLIC_URL:=}"
+: "${DEVDESK_MATRIX_WEBHOOK_FILE:=/etc/devdesk/matrix-webhook}"
+: "${DEVDESK_MATRIX_DELAY:=30}"
 
 DEVDESK_REGISTRY="$DEVDESK_STATE_DIR/registry.json"
 DEVDESK_CONTEXT_DIR="$DEVDESK_STATE_DIR/context"