feat: comprehensive code review fixes + receivers-only architecture

Security:
- Refuse startup with default secret_key in production (was just logging)
- Settings endpoint now requires admin role
- Password validation on initial setup
- DOM-based HTML sanitizer replaces regex in template previews
- Add *.log to .gitignore

Performance & reliability:
- Token refresh deduplication prevents race condition on concurrent 401s
- Theme media query listener registered once (no leak)
- IconPicker uses $derived instead of function call per render
- Snackbar uses single-batch state update instead of while loop
- Replace 11 inline hover handlers with CSS :hover in layout

Architecture - receivers-only:
- Delivery endpoints (chat_id, email, url, room_id, topic) now stored
  exclusively in TargetReceiver rows, never in target.config
- Migration extracts existing delivery fields to receiver rows
- Notifier and dispatcher remove all config fallbacks
- Frontend targets page shows receivers list per target with
  add/remove/toggle/test per receiver
- Single-receiver test endpoint: POST /targets/{id}/receivers/{id}/test

Code quality:
- Extract AuthLayout.svelte from login/setup (150 lines CSS dedup)
- Split telegram-bots page (754→51 lines + 3 tab components)
- Split notification-trackers page (547→432 lines + 4 components)
- Deduplicate _send_reply into shared handler.send_reply()
- Add locale column to template models, replace name-based detection
- Fix delete_notification_tracker dead protection check
- Fix check_telegram_bot query (filter by type, remove bogus OR)
- Add graceful scheduler shutdown in lifespan
- Consistent /bots?tab=telegram URLs across all nav links

i18n:
- Error page, chat actions, target types, provider types internationalized
- All new receiver UI strings in EN + RU

frontend/src/routes/notification-trackers/LinkedTargetsSection.svelte

@@ -0,0 +1,119 @@
+<script lang="ts">
+	import { slide } from 'svelte/transition';
+	import { t } from '$lib/i18n';
+	import MdiIcon from '$lib/components/MdiIcon.svelte';
+	import IconButton from '$lib/components/IconButton.svelte';
+	import type { Tracker, NotificationTarget, TrackingConfig, TemplateConfig } from '$lib/types';
+
+	interface Props {
+		tracker: Tracker;
+		trackingConfigs: TrackingConfig[];
+		templateConfigs: TemplateConfig[];
+		unlinkedTargets: NotificationTarget[];
+		newLinkTargetId: number;
+		newLinkTrackingConfigId: number;
+		newLinkTemplateConfigId: number;
+		addingTarget: boolean;
+		ttTesting: Record<string, string>;
+		configsForTracker: (configs: (TrackingConfig | TemplateConfig)[]) => any[];
+		onupdateLink: (tt: any, field: string, value: any) => void;
+		onremoveLink: (ttId: number) => void;
+		onaddLink: () => void;
+		onopenTestMenu: (ttId: number, event: MouseEvent) => void;
+		onchangeNewTarget: (value: number) => void;
+		onchangeNewTrackingConfig: (value: number) => void;
+		onchangeNewTemplateConfig: (value: number) => void;
+	}
+
+	let {
+		tracker,
+		trackingConfigs,
+		templateConfigs,
+		unlinkedTargets,
+		newLinkTargetId,
+		newLinkTrackingConfigId,
+		newLinkTemplateConfigId,
+		addingTarget,
+		ttTesting,
+		configsForTracker,
+		onupdateLink,
+		onremoveLink,
+		onaddLink,
+		onopenTestMenu,
+		onchangeNewTarget,
+		onchangeNewTrackingConfig,
+		onchangeNewTemplateConfig,
+	}: Props = $props();
+</script>
+
+<div class="mt-3 border-t border-[var(--color-border)] pt-3 space-y-2" in:slide>
+	{#if (tracker.tracker_targets || []).length === 0}
+		<p class="text-xs text-[var(--color-muted-foreground)]">{t('notificationTracker.noLinkedTargets')}</p>
+	{:else}
+		{#each tracker.tracker_targets as tt}
+			<div class="flex items-center justify-between text-sm px-2 py-1.5 rounded bg-[var(--color-muted)]/30">
+				<div class="flex items-center gap-2">
+					<span style="color: var(--color-primary);"><MdiIcon name={tt.target_icon || (tt.target_type === 'telegram' ? 'mdiSend' : 'mdiWebhook')} size={16} /></span>
+					<span class="font-medium">{tt.target_name || `Target #${tt.target_id}`}</span>
+					<span class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-muted)] text-[var(--color-muted-foreground)]">{tt.target_type}</span>
+					{#if !tt.enabled}
+						<span class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-warning-bg)] text-[var(--color-warning-fg)]">{t('notificationTracker.paused')}</span>
+					{/if}
+				</div>
+				<div class="flex items-center gap-2 flex-wrap justify-end">
+					<select value={tt.tracking_config_id || 0}
+						onchange={(e: Event) => onupdateLink(tt, 'tracking_config_id', Number((e.target as HTMLSelectElement).value) || null)}
+						class="text-xs px-2 py-1 border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
+						<option value={0}>— {t('trackingConfig.title')} —</option>
+						{#each configsForTracker(trackingConfigs) as tc}<option value={tc.id}>{tc.name}</option>{/each}
+					</select>
+					<select value={tt.template_config_id || 0}
+						onchange={(e: Event) => onupdateLink(tt, 'template_config_id', Number((e.target as HTMLSelectElement).value) || null)}
+						class="text-xs px-2 py-1 border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
+						<option value={0}>— {t('templateConfig.title')} —</option>
+						{#each configsForTracker(templateConfigs) as tc}<option value={tc.id}>{tc.name}</option>{/each}
+					</select>
+					<div class="relative">
+						<IconButton icon="mdiDotsVertical" size={14} title={t('common.test')}
+							onclick={(e: MouseEvent) => onopenTestMenu(tt.id, e)}
+							disabled={Object.keys(ttTesting).some(k => k.startsWith(`${tt.id}_`) && ttTesting[k])} />
+					</div>
+					<IconButton icon={tt.enabled ? 'mdiPause' : 'mdiPlay'} size={14}
+						title={tt.enabled ? t('notificationTracker.pause') : t('notificationTracker.resume')}
+						onclick={() => onupdateLink(tt, 'enabled', !tt.enabled)} />
+					<IconButton icon="mdiClose" size={14} title={t('common.delete')}
+						onclick={() => onremoveLink(tt.id)} variant="danger" />
+				</div>
+			</div>
+		{/each}
+	{/if}
+
+	<!-- Add target link -->
+	{#if unlinkedTargets.length > 0}
+		<div class="flex items-center gap-2 mt-2">
+			<select value={newLinkTargetId}
+				onchange={(e: Event) => onchangeNewTarget(Number((e.target as HTMLSelectElement).value))}
+				class="text-xs px-2 py-1 border border-[var(--color-border)] rounded-md bg-[var(--color-background)] flex-1">
+				<option value={0}>— {t('notificationTracker.addTarget')} —</option>
+				{#each unlinkedTargets as tgt}<option value={tgt.id}>{tgt.name} ({tgt.type})</option>{/each}
+			</select>
+			<select value={newLinkTrackingConfigId}
+				onchange={(e: Event) => onchangeNewTrackingConfig(Number((e.target as HTMLSelectElement).value))}
+				class="text-xs px-2 py-1 border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
+				<option value={0}>— {t('trackingConfig.title')} —</option>
+				{#each configsForTracker(trackingConfigs) as tc}<option value={tc.id}>{tc.name}</option>{/each}
+			</select>
+			<select value={newLinkTemplateConfigId}
+				onchange={(e: Event) => onchangeNewTemplateConfig(Number((e.target as HTMLSelectElement).value))}
+				class="text-xs px-2 py-1 border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
+				<option value={0}>— {t('templateConfig.title')} —</option>
+				{#each configsForTracker(templateConfigs) as tc}<option value={tc.id}>{tc.name}</option>{/each}
+			</select>
+			<button onclick={onaddLink}
+				disabled={!newLinkTargetId || addingTarget}
+				class="text-xs px-3 py-1 bg-[var(--color-primary)] text-[var(--color-primary-foreground)] rounded hover:opacity-90 disabled:opacity-50">
+				{t('common.add')}
+			</button>
+		</div>
+	{/if}
+</div>