feat(telegram): add 'none' listener mode for bots

Introduce a third update_mode option alongside polling/webhook. 'none'
disables both polling and webhook delivery — useful when another instance
owns the listener or when the bot is send-only. Switching into 'none' now
unschedules polling and unregisters any active webhook so Telegram stops
delivering updates.

New bots default to 'none' (safer when multiple bridges share a token).
Existing bots upgraded from a pre-update_mode schema keep 'polling' so
their behavior is unchanged.

frontend/src/lib/i18n/en.json

@@ -433,6 +433,8 @@
 		"webhookRegistered": "Webhook registered",
 		"webhookUnregistered": "Webhook unregistered",
 		"updateMode": "Update mode",
+		"none": "None",
+		"noneActive": "Listener disabled",
 		"polling": "Polling",
 		"webhook": "Webhook",
 		"webhookStatus": "Webhook status",

frontend/src/lib/i18n/ru.json

@@ -433,6 +433,8 @@
 		"webhookRegistered": "Вебхук зарегистрирован",
 		"webhookUnregistered": "Вебхук удалён",
 		"updateMode": "Режим обновлений",
+		"none": "Откл.",
+		"noneActive": "Приём обновлений отключён",
 		"polling": "Опрос",
 		"webhook": "Вебхук",
 		"webhookStatus": "Статус вебхука",

frontend/src/routes/bots/TelegramBotTab.svelte

@@ -334,10 +334,12 @@
 								<span class="text-xs text-[var(--color-muted-foreground)]">@{bot.bot_username}</span>
 							{/if}
 							<!-- Mode badge -->
-							<span class="text-xs px-1.5 py-0.5 rounded font-mono {bot.update_mode === 'webhook'
+							<span class="text-xs px-1.5 py-0.5 rounded font-mono {(bot.update_mode || 'none') === 'webhook'
 								? 'bg-[var(--color-primary)]/10 text-[var(--color-primary)]'
-								: 'bg-[var(--color-success-bg)] text-[var(--color-success-fg)]'}">
-								{bot.update_mode === 'webhook' ? t('telegramBot.webhook') : t('telegramBot.polling')}
+								: (bot.update_mode || 'none') === 'polling'
+									? 'bg-[var(--color-success-bg)] text-[var(--color-success-fg)]'
+									: 'bg-[var(--color-muted)] text-[var(--color-muted-foreground)]'}">
+								{(bot.update_mode || 'none') === 'webhook' ? t('telegramBot.webhook') : (bot.update_mode || 'none') === 'polling' ? t('telegramBot.polling') : t('telegramBot.none')}
 							</span>
 						</div>
 						<p class="text-xs text-[var(--color-muted-foreground)] font-mono">{bot.token_preview}</p>
@@ -456,6 +458,14 @@
 							<p class="text-xs font-medium mb-2">{t('telegramBot.updateMode')}</p>
 							<div class="flex items-center gap-3 flex-wrap">
 								<div class="flex items-center rounded-md border border-[var(--color-border)] overflow-hidden">
+									<button onclick={() => switchMode(bot.id, 'none')}
+										disabled={modeChanging[bot.id] || (bot.update_mode || 'none') === 'none'}
+										class="px-3 py-1 text-xs transition-colors {(bot.update_mode || 'none') === 'none'
+											? 'bg-[var(--color-primary)] text-[var(--color-primary-foreground)]'
+											: 'hover:bg-[var(--color-muted)]'} disabled:opacity-70">
+										<MdiIcon name="mdiBellOff" size={14} />
+										{t('telegramBot.none')}
+									</button>
 									<button onclick={() => switchMode(bot.id, 'polling')}
 										disabled={modeChanging[bot.id] || bot.update_mode === 'polling'}
 										class="px-3 py-1 text-xs transition-colors {bot.update_mode === 'polling'
@@ -474,6 +484,13 @@
 									</button>
 								</div>
 
+								{#if (bot.update_mode || 'none') === 'none'}
+									<span class="text-xs text-[var(--color-muted-foreground)] flex items-center gap-1">
+										<MdiIcon name="mdiBellOff" size={14} />
+										{t('telegramBot.noneActive')}
+									</span>
+								{/if}
+
 								{#if bot.update_mode === 'polling'}
 									<span class="text-xs text-[var(--color-success-fg)] flex items-center gap-1">
 										<MdiIcon name="mdiCheckCircle" size={14} />