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/lib/i18n/en.json

@@ -262,7 +262,14 @@
 		"testPeriodic": "Test periodic summary",
 		"testScheduled": "Test scheduled assets",
 		"testMemory": "Test memory / On This Day",
+		"testDisabledHint": "Enable this feature in the tracker's default Tracking Config first.",
 		"checkingLinks": "Checking links...",
+		"featureDiscovery": "Configure periodic summaries, scheduled photo picks, memories, and quiet hours in the default Tracking Config.",
+		"openTrackingConfig": "Open Tracking Config",
+		"linkReplace": "Replace",
+		"linkReplacing": "Replacing...",
+		"linkReplaceFailed": "Failed to replace link for \"{name}\"",
+		"linkPasswordProtectedNote": "Telegram users can't open password-protected links without the password. Remove the password in Immich or replace the link.",
 		"missingLinksTitle": "Albums Missing Public Links",
 		"missingLinksDesc": "The following albums don't have public shared links. Without links, notification recipients won't be able to view photos.",
 		"expired": "Expired",
@@ -552,7 +559,14 @@
 		"renamed": "renamed",
 		"deleted": "deleted",
 		"providerType": "Provider Type",
-		"sortRandom": "Random"
+		"sortRandom": "Random",
+		"timesInlineHelp": "HH:MM, comma-separated",
+		"invalidTimeList": "Use HH:MM format, e.g. 09:00 or 09:00, 18:30",
+		"previewTemplate": "Preview template",
+		"previewSampleNote": "Rendered with sample data — not your real assets. Shows the shipped default template.",
+		"editTemplate": "Edit template",
+		"quietHoursZero": "Quiet period is 0 minutes — adjust times",
+		"nextDay": "next day"
 	},
 	"templateConfig": {
 		"title": "Template Configs",
@@ -598,7 +612,14 @@
 		"confirmDelete": "Delete this template config?",
 		"invalidFormat": "Invalid format string",
 		"filterSlots": "Filter slots...",
-		"slots": "slots"
+		"slots": "slots",
+		"resetToDefault": "Reset to default",
+		"resetAllToDefaults": "Reset all to defaults",
+		"resetSlotConfirm": "Replace this slot's {locale} template with the shipped default? Your current edits will be lost.",
+		"resetAllConfirm": "Replace every slot's {locale} template with the shipped defaults? All your {locale} edits will be lost.",
+		"resetNoDefault": "No shipped default for this slot.",
+		"resetApplied": "Reset to default (not saved yet — click Save to persist)",
+		"deepLinkNoConfig": "No template config found for this provider. Create one first."
 	},
 	"templateVars": {
 		"message_assets_added": {
@@ -715,9 +736,12 @@
 		"quietHours": "Suppress all notifications during this HH:MM window (interpreted in the app timezone). Overnight windows like 22:00–07:00 are supported.",
 		"favoritesOnly": "Only include assets marked as favorites.",
 		"maxAssets": "Maximum number of asset details to include in a single notification message.",
-		"periodicStartDate": "The reference date for calculating periodic intervals. Summaries are sent every N days from this date.",
+		"periodicStartDate": "Reference date in the app timezone. The first summary fires at the next configured HH:MM on/after this date, then every N days.",
+		"intervalDays": "Days between successive summaries. 1 = daily, 7 = weekly.",
 		"times": "Time(s) of day to send notifications, in HH:MM format. Use commas for multiple times: 09:00,18:00",
 		"albumMode": "Per album: separate notification per album. Combined: one notification with all albums. Random: pick one album randomly.",
+		"scheduledAlbumMode": "How albums are grouped in scheduled deliveries. Default: Per album (one notification per tracked album).",
+		"memoryAlbumMode": "How albums are grouped in memory deliveries. Default: Combined (a single notification aggregating matches from all tracked albums).",
 		"minRating": "Only include assets with at least this star rating (0 = no filter).",
 		"eventMessages": "Templates for real-time event notifications. Use {variables} for dynamic content.",
 		"assetFormatting": "How individual assets are formatted within notification messages.",