feat: v0.9.0 conversation search, plan usage meters, quiet phone at the desk

- devdesk attach --search (grep + jq over ~/.claude/projects, six files at
  a time) and --resume-convo NAME ID [fork]; devdesk-claude-run passes
  --fork-session once. Search dialog with Resume / Fork / Open.
- statusLine snapshots rate_limits and pr; footer/menu meters with a 90 %
  warning; PR chip on session rows.
- CLAUDE_CLIENT_PRESENCE_FILE per tmux session id; --presence on|off with a
  self-expiring marker; the page heartbeats it while visible.

Closes #24
Closes #25
Closes #26

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

libexec/devdesk-lib.sh

@@ -37,6 +37,7 @@ dd_load_env
 : "${DEVDESK_PUBLIC_URL:=}"
 : "${DEVDESK_MATRIX_WEBHOOK_FILE:=/etc/devdesk/matrix-webhook}"
 : "${DEVDESK_MATRIX_DELAY:=30}"
+: "${DEVDESK_PRESENCE_DIR:=/run/devdesk/presence}"
 
 DEVDESK_REGISTRY="$DEVDESK_STATE_DIR/registry.json"
 DEVDESK_CONTEXT_DIR="$DEVDESK_STATE_DIR/context"