feat(daemon): deliver stop reliably and never kill the node unasked

Closing the wallet sent "stop" at most twice, gated on a getinfo probe
that needs the daemon's cs_main, then killed the node after 20 s (Windows)
or 30 s (POSIX) whether or not stop had arrived. A node busy with an
hour-long witness rebuild therefore never got stop, was killed mid-
rebuild, and replayed everything since its last flush on every start.

Delivery (src/daemon/stop_delivery.h, RPCClient::open/trySendStop):
- stop goes over a dedicated client with no probe, so it never waits on
  rpc_'s lock or a cs_main-bound getinfo
- every attempt is classified, and StopDeliveryPolicy decides the next:
  Accepted / 503 = delivered; Queued (reply timeout) is resent at most
  every 30 s; QueueFull / not listening are retried every 1.5 s; a
  refusal after we were heard means the node is shutting down; a 401 on
  our own node tries the next credential source
- POSIX: a group SIGTERM goes out as soon as an attempt fails, which
  bypasses the HTTP queue entirely

Waiting (DaemonController::executeDaemonStop, pure, virtual-clock
tested):
- never kills on its own. Quitting waits as long as the node needs; the
  shutdown screen offers "Close wallet — leave node running" after 3 s,
  and "Kill node (unsafe)" (confirmed) only once stop was delivered and
  the node showed no CPU/I-O progress for ~10 min outside a rebuild
- other callers (restart, rescan, reinstall, switch, ...) wait up to
  120 s, let go once the app starts quitting, and keep watching a node
  that is still running; wallet switch refuses to go ahead then
- EmbeddedDaemon gains stop-session primitives (beginStop,
  pollOwnedProcess, signalGracefulStop, forceKillOwnedProcess,
  ownedResourceUsage over the Linux process group / Windows handle,
  endStop) and only one stop session runs at a time
- the Force Quit button and its stall heuristic are gone; "Leave
  running" aborts a pending stop attempt and closes at once

Verified against the fake daemon with the real GUI: closing mid-rebuild
now delivers stop (or SIGTERM 2 ms after a queue-full refusal) and the
node exits cleanly after its rebuild, where it was SIGKILLed before. The
shutdown screen, its "Leave running" button and the idle Kill offer
(after ~11 min) were checked by screenshot. New strings are English-
only for now.

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

src/util/i18n.cpp

@@ -587,6 +587,19 @@ void I18n::loadBuiltinEnglish()
         strings_["force_quit_confirm_title"] = "Force Quit?";
         strings_["force_quit_confirm_msg"] = "This will immediately kill the daemon without a clean shutdown.\nThis may corrupt the blockchain index and require a resync.";
         strings_["force_quit_yes"] = "Force Quit";
+        // Stopping the node on quit: deliver stop, wait, never kill unasked (translations: S10 batch)
+        strings_["shutdown_leave_running"] = "Close wallet — leave node running";
+        strings_["shutdown_leave_running_tip"] = "Closes the wallet now. The node keeps running and finishes shutting down on its own; nothing is lost.";
+        strings_["shutdown_kill_node"] = "Kill node (unsafe)";
+        strings_["shutdown_kill_node_tip"] = "Ends the node at once. Anything it has not saved is lost, and its next start replays the blocks since its last save.";
+        strings_["shutdown_kill_confirm_title"] = "Kill the node?";
+        strings_["shutdown_kill_confirm_msg"] = "The node has shown no CPU or disk activity for a long time and may be stuck.\nKilling it loses everything it has not saved; its next start can take much longer.";
+        strings_["shutdown_kill_confirm_yes"] = "Kill node";
+        strings_["shutdown_stop_asking"] = "Asking the node to stop…";
+        strings_["shutdown_stop_queued"] = "The node has the stop request but is busy — it will stop when it can";
+        strings_["shutdown_stop_delivered"] = "The node is shutting down and saving its state";
+        strings_["shutdown_stop_cpu_suffix"] = " · CPU %d%%";
+        strings_["shutdown_stop_idle"] = "No CPU or disk activity for %d min — the node may be stuck";
         strings_["reduce_motion"] = "Reduce Motion";
         strings_["tt_reduce_motion"] = "Disable animated transitions and balance lerp for accessibility";
         strings_["ago"] = "ago";