vc=32: subs feed — dates, watched filter, infinite scroll, avatar fallback

Subscription feed is now actually a feed instead of a teaser.

Rust (strawcore wrapper)
  Added upload_date_relative and uploader_avatar to SearchItem so
  Kotlin can see both. strawcore-core already extracts upload_date
  relative ("2 days ago") on every StreamInfoItem and uploader_avatars
  on most — we were just throwing them away in from_core. Fixed.

StreamItem
  uploadDateRelative + uploaderAvatar fields added. Every construction
  site (search/channel/detail/feed) plumbs them through.

SubscriptionFeedViewModel
  Per-channel cap 5 → 30. With 30 subs that's up to 900 items in
  memory; ConcurrentHashMap entries are small enough.
  Sort by parsed relative recency (RECENCY_RE on the "N <unit> ago"
  string, signed seconds-ago, tied items break by viewCount).
  Opportunistic avatar backfill: every successful channelInfo fetch
  updates the stored ChannelRef.avatar via Subscriptions.updateAvatar
  when strawcore returns a non-null avatar — fixes the "I just subbed
  to a channel and the chip has no icon" case where the channel header
  parser missed the avatar at subscribe time but the feed-fetch
  layout returns one.

SubsPane (StrawHome)
  Hide-watched FilterChip (session-sticky). Cross-references
  History.watches by 11-char YT video ID; filters out anything you've
  already watched. "All caught up — nothing unwatched" empty state.
  Infinite scroll: PAGE_SIZE = 20. derivedStateOf-gated snapshotFlow
  watches the LazyListState's lastVisibleItem index; when within 5
  items of the bottom, bumps visibleCount by 20. "Loading more..."
  spinner at the bottom while there's more to show.
  Visible-count resets to PAGE_SIZE when the underlying list shrinks
  (refresh dropped items, filter just engaged).
  FeedRow now shows: uploader · views · "3 days ago".

SubChip
  Lettered fallback when ch.avatar is null. PrimaryContainer-tinted
  circle with the first letter — no more broken-image placeholder
  while the feed-fetch backfills the real avatar.

SubscriptionsStore
  updateAvatar(url, avatar) for the backfill path. Atomic via
  updateAndGet, persists to SharedPreferences.

rust/strawcore/src/search.rs

@@ -15,11 +15,16 @@ pub struct SearchItem {
     pub title: String,
     pub uploader: String,
     pub uploader_url: Option<String>,
+    pub uploader_avatar: Option<String>,
     pub thumbnail: Option<String>,
     /// Duration in seconds. 0 = live/unknown.
     pub duration_seconds: i64,
     /// Reported view count. 0 = unknown.
     pub view_count: i64,
+    /// Relative upload date as YT renders it ("2 days ago", "3 weeks
+    /// ago"). Empty if not extracted. Strawcore-core already populates
+    /// this on StreamInfoItem; we just pass it through.
+    pub upload_date_relative: String,
 }
 
 pub(crate) fn from_core(item: StreamInfoItem) -> SearchItem {
@@ -32,11 +37,16 @@ pub(crate) fn from_core(item: StreamInfoItem) -> SearchItem {
         .thumbnails
         .last()
         .map(|i| i.url().to_string());
+    let uploader_avatar = item
+        .uploader_avatars
+        .last()
+        .map(|i| i.url().to_string());
     SearchItem {
         url: item.url,
         title: item.name,
         uploader: item.uploader_name,
         uploader_url,
+        uploader_avatar,
         thumbnail,
         duration_seconds: item.duration_seconds,
         view_count: if item.view_count < 0 {
@@ -44,6 +54,7 @@ pub(crate) fn from_core(item: StreamInfoItem) -> SearchItem {
         } else {
             item.view_count
         },
+        upload_date_relative: item.upload_date_relative,
     }
 }