feat: replace modal user-confirm dialog with persistent flashing button

Both clients used a modal OK dialog for a Sud step's WAIT_USER
confirmation (e.g. "Bitte Malz einfuellen und bestaetigen"). Replaced
with a persistent "Confirm" control in the top toolbar/header instead:
flashes yellow with the step's message while pending, and modally
disables the rest of the GUI (main content plus Start/Pause/Stop/
New/Save/Load, and Connect) until it's clicked - forcing the pending
step to be dealt with first. Disabled and blank otherwise.

client/brewpi_gui.py: set_user_confirm_pending() drives a QTimer blink
(same pattern as the existing "Cool down" indicator) and disables
centralwidget + the relevant toolbar QActions individually, so the new
button (a toolbar sibling) stays enabled; Start/Pause/Stop are restored
via update_sud_actions() rather than a blanket re-enable.

web/app.js: setUserConfirmPending() toggles a 'confirm-pending' class
(CSS @keyframes flash, matching the file's existing animation-by-class
convention) and a 'modally-disabled' class on #layout; also wired into
ws.onclose so a dropped connection doesn't leave the page stuck modally
disabled on a confirm that'll never resolve.

Also fixes a message-ordering race in both clients (found testing the
web version on an iPad, connecting fresh while a step was already
WAIT_USER): a step's UserMessage is set once when the step starts, well
before State later flips to WAIT_USER, so an already-connected client
sees them at genuinely different times - but a client connecting fresh
gets both bundled into one replayed snapshot, where State's key can
sort before UserMessage's. Processing State first checked the pending
guard before that same message had set the text, silently failing it
and leaving the button looking merely disabled. Both onSudChanged()/
on_sud_changed() now force UserMessage (and, in the web client, Json)
to process before State/Step regardless of the bundled dict's key
order, same pattern already used for the pre-existing Json-before-Step
case.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M2ierBoxW3v7nUbDw3M2pE

web/index.html

@@ -30,6 +30,10 @@
 		<input type="file" id="sud-file-input" accept="application/json" class="hidden">
 		<button id="btn-sud-save">Save&hellip;</button>
 	</div>
+	<div id="user-confirm-row">
+		<span id="user-confirm-text"></span>
+		<button id="btn-user-confirm" type="button" disabled>Confirm</button>
+	</div>
 </header>
 
 <main id="layout">
@@ -286,13 +290,6 @@
 
 </main>
 
-<dialog id="sud-message-dialog">
-	<p id="sud-message-text"></p>
-	<form>
-		<button id="sud-message-ok" type="button">OK</button>
-	</form>
-</dialog>
-
 <footer>
 	<div id="sud-status-line"></div>
 	<div id="env-status-line"></div>