panel: redesign web UI and make syncing responsive

Web UI (panel/frontend/index.html) rewritten:
- Cards update in place from a single /status poll instead of being rebuilt
  on every action, so open tabs, unsaved compose/route edits, logs and the
  file browser position survive refreshes. Polling speeds up while an
  operation runs and pauses in background tabs; a header indicator shows
  when the panel last synced and detects an expired Authelia session.
- New-app dialog (starter / compose / git), suggested port and domain,
  proper confirm dialogs (the old "OK = keep volumes" remove prompt is gone),
  toasts, an activity drawer with operation output, overflow menu, search,
  status filters, keyboard shortcuts, deep links, dark mode and mobile layout.
- Tabs: overview (containers + routes), compose editor (dirty tracking,
  Ctrl+S), logs with follow, validated routes editor, file browser with
  drag-and-drop upload, backups, and a git source tab (deployed commit,
  check for updates, sync & deploy).

API (panel/panel-api.py):
- ThreadingHTTPServer so a long deploy no longer blocks every other request.
- Per-app operation lock; concurrent writes to a busy app return 409.
- GET /status: all apps, routes and container status in one request
  (statuses gathered in parallel); status reports running/partial/stopped.
- Git sync is fetch + hard reset instead of pull-or-reclone, keeps the stored
  token, reports before/after commits; GET /apps/<name>/repo[?fetch=1].
- Any http(s) git host (e.g. Forgejo), default branch detection, git
  timeouts, no credential prompts, tokens redacted from errors, and manifest
  values validated before being written into the bash-sourced manifest.

panelctl:
- flock around routes.caddy rewrites (util-linux added to the service path).
- deploy returns compose output so failures are visible in the UI.
- inspect-volumes no longer fails for apps without named podman volumes,
  which broke the file browser.

Docs: README/API.md updated; fixed outdated panelctl init examples.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UbWSNkXxZhYf7eqHTyx3Bf

panelctl.sh

@@ -149,6 +149,19 @@ app_route_file() {
   echo "${ROUTES_DIR}/routes.caddy"
 }
 
+# The routes file is shared by all apps and rewritten read-modify-write, so
+# concurrent panelctl runs (the API handles requests in parallel) must take turns.
+routes_lock() {
+  exec 9>"${ROUTES_DIR}/.routes.lock"
+  if command -v flock >/dev/null 2>&1; then
+    flock -w 30 9 || fail "timed out waiting for the routes file lock"
+  fi
+}
+
+routes_unlock() {
+  exec 9>&-
+}
+
 load_app() {
   local name="$1"
   local manifest
@@ -337,6 +350,8 @@ cmd_render_route() {
   local route_file
   route_file="$(app_route_file)"
 
+  routes_lock
+
   # Strip any existing block for this app from the aggregate file.
   local tmp
   tmp="$(mktemp)"
@@ -376,6 +391,8 @@ cmd_render_route() {
   } >>"${tmp}"
 
   install -m 0664 -o reudy -g panelroutes "${tmp}" "${route_file}"
+  rm -f "${tmp}"
+  routes_unlock
   log info "rendered route ${route_file}"
 }
 
@@ -388,10 +405,17 @@ cmd_deploy() {
 
   cmd_render_route "${name}"
 
-  if ! run_compose -f "${APP_COMPOSE_FILE}" up -d --build --remove-orphans 2>&1 | systemd-cat -t panelctl -p info 2>/dev/null; then
+  # Capture compose output so callers (the web UI) can show why a deploy failed,
+  # and still forward it to the journal.
+  local output
+  if ! output="$(run_compose -f "${APP_COMPOSE_FILE}" up -d --build --remove-orphans 2>&1)"; then
+    printf '%s\n' "${output}" | systemd-cat -t panelctl -p err 2>/dev/null || true
+    printf '%s\n' "${output}" >&2
     log err "Deployment failed for app '${name}'"
     fail "compose up failed"
   fi
+  printf '%s\n' "${output}" | systemd-cat -t panelctl -p info 2>/dev/null || true
+  printf '%s\n' "${output}"
 
   log info "Successfully deployed app '${name}'"
 }
@@ -479,10 +503,13 @@ cmd_remove() {
   local route_file
   route_file="$(app_route_file)"
   if [[ -f "${route_file}" ]]; then
+    routes_lock
     local tmp
     tmp="$(mktemp)"
     sed "/^# route:${name}:start$/,/^# route:${name}:end$/d" "${route_file}" >"${tmp}" || true
     install -m 0664 -o reudy -g panelroutes "${tmp}" "${route_file}"
+    rm -f "${tmp}"
+    routes_unlock
   fi
 
   rm -f "$(app_manifest "${name}")"
@@ -671,7 +698,8 @@ cmd_inspect_volumes() {
   if [[ -n "${podman_bin}" ]]; then
     "${podman_bin}" volume ls --filter label=com.docker.compose.project="${name}" --format '{{.Name}}|{{.Mountpoint}}' 2>/dev/null || true
     "${podman_bin}" volume ls --filter label=io.podman.compose.project="${name}" --format '{{.Name}}|{{.Mountpoint}}' 2>/dev/null || true
-  fi | sort -u | grep -v '^$'
+  # grep exits 1 when there are no named volumes; that is not an error.
+  fi | sort -u | grep -v '^$' || true
 }
 
 cmd_list() {