Mobile notifications for iOS (#210)

* mobile: wire notification registration and listener

* implement backend components for push notifications

* refactor: agentic comment cleanup

* docs: use proper module name for particle processor

* set required env variables for push notifications

* bump version

* fix: always upsert push token on mobile start

* Revert "fix: always upsert push token on mobile start"

This reverts commit 90ff18a788.

* send push notifications regardless of online status

go/cmd/transcodebackfill/main.go

@@ -1,12 +1,6 @@
-// transcodebackfill is a one-shot job that scans every doc under the
-// "children" Firestore collection group, identifies media particles missing a
-// transcoded variant, and re-runs the transcode + upload + Firestore-update
-// flow against the configured GCS bucket. Idempotent — re-running the Job
-// after a partial failure picks up where it left off via the existing
-// `transcoded_object_id != ""` short-circuit inside particle.Transcode.
-//
-// Intended to back-fill the production iOS playback backlog created before we
-// launched mobile / particle processor worker only transcodes new media.
+// transcodebackfill walks every doc under the "children" collection group and
+// re-runs transcode for media particles missing a transcoded variant.
+// Idempotent: particle.Transcode short-circuits on transcoded_object_id != "".
 package main
 
 import (
@@ -104,9 +98,7 @@ func run(ctx context.Context, fs *firestore.Client, depotSvc depot.Service) (sta
 
 		s.scanned++
 
-		// Cheap pre-filter: most docs under the "children" collection group
-		// are not media particles. DataAt avoids unmarshalling the full
-		// document for those.
+		// DataAt avoids unmarshalling the full doc; most children aren't media.
 		rawType, err := doc.DataAt("type")
 		if err != nil {
 			s.skippedNonMedia++