feat(immich): per-album scheduled/memory dispatch + template tooling

Dispatch: honor {kind}_collection_mode on TrackingConfig — "per_collection"
fans out one event per album; "combined" pools assets as before. Extract
build_immich_dispatch_events shared by cron and test paths.

Assets: collect_scheduled_assets attaches album_name/album_url/album_public_url
to each asset so combined-mode templates can attribute rows to their source
album. Default scheduled_assets templates render a multi-album header with
inline album list and per-row album link; memory_mode follows the same pattern.

UI: "Reset to default" buttons on notification and command template slots
(per-slot and whole-template), backed by new GET /*-template-configs/defaults
endpoints. tracking-configs "Preview template" now opens an inline preview
modal with locale tabs instead of navigating away; Edit button deep-links
with ?edit_slot=<name> so the destination auto-opens the config and scrolls
to the slot. Reset confirmations use ConfirmModal instead of window.confirm.

Fixes:
* NotificationDispatcher._session_ctx infinite recursion when no shared
  aiohttp.ClientSession was passed — broke test dispatch for periodic/
  scheduled/memory (cron path was unaffected).
* telegram-bots /chats/{id}/test now resolves chat.language_override /
  language_code instead of using the raw ?locale query param, matching
  the resolution the tracker-target test endpoint already used.
* scheduled_assets default template no longer emits a blank line between
  header and the first asset when the multi-album branch is taken.

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

@@ -4,6 +4,7 @@
 	import Card from '$lib/components/Card.svelte';
 	import IconPicker from '$lib/components/IconPicker.svelte';
 	import Hint from '$lib/components/Hint.svelte';
+	import MdiIcon from '$lib/components/MdiIcon.svelte';
 	import EntitySelect from '$lib/components/EntitySelect.svelte';
 	import MultiEntitySelect from '$lib/components/MultiEntitySelect.svelte';
 	import { getDescriptor } from '$lib/providers';
@@ -199,6 +200,22 @@
 		</div>
 		{/if}
 
+		<!-- Feature discovery: the periodic/scheduled/memory/quiet-hours controls
+		     live on the tracking config, not on the tracker itself. Surface this
+		     here so users don't have to stumble onto the feature by reading docs. -->
+		{#if providerType === 'immich'}
+		<div class="flex items-start gap-2 rounded-md border border-[var(--color-border)] bg-[var(--color-muted)]/30 px-3 py-2">
+			<span style="color: var(--color-primary);"><MdiIcon name="mdiInformationOutline" size={16} /></span>
+			<div class="flex-1 text-xs">
+				<p style="color: var(--color-muted-foreground);">{t('notificationTracker.featureDiscovery')}</p>
+				<a href="/tracking-configs" class="inline-flex items-center gap-1 text-[var(--color-primary)] hover:underline mt-1">
+					<MdiIcon name="mdiArrowRight" size={12} />
+					{t('notificationTracker.openTrackingConfig')}
+				</a>
+			</div>
+		</div>
+		{/if}
+
 		<button type="submit" disabled={submitting || linkCheckLoading} class="px-4 py-2 bg-[var(--color-primary)] text-[var(--color-primary-foreground)] rounded-md text-sm font-medium hover:opacity-90 disabled:opacity-50">
 			{#if linkCheckLoading}{t('notificationTracker.checkingLinks')}{:else}{editing ? t('common.save') : t('notificationTracker.createTracker')}{/if}
 		</button>