feat(i18n): every server A→Z list in the reader's alphabet (E30 S3)

The Postgres image is Alpine, whose en_US.utf8 is byte order: "Életrajzi" and
"Ötödik" sorted after "Zorró" in the feed, the channel lists, the Plex grid,
its genres and collections. `app/collation.py` names the ICU collation of the
reader's language (hu-x-icu puts "Ö" after "O" and "Cs" after "Cu"), wraps
every text ORDER BY with it - the feed's keyset cursor compares with the same
expression, so paging walks the order it sorted in - and orders the lists built
in Python (genre and studio facets, collection members, the discovery re-sort)
through the same collation. Plex title tiebreaks use the shown (HU) title.

backend/app/routes/channels.py

@@ -9,6 +9,8 @@ from pydantic import BaseModel
 from sqlalchemy import func, select, update
 from sqlalchemy.orm import Session
 
+from app.collation import collated, sorted_words
+from app.mailtext import lang_for_user
 from app import logs, quota
 from app.auth import admin_user, current_user, require_human, require_write_scope
 from app.db import get_db
@@ -44,7 +46,7 @@ def list_channels(user: User = Depends(current_user), db: Session = Depends(get_
         select(Subscription, Channel)
         .join(Channel, Channel.id == Subscription.channel_id)
         .where(Subscription.user_id == user.id)
-        .order_by(Subscription.priority.desc(), func.lower(Channel.title))
+        .order_by(Subscription.priority.desc(), collated(Channel.title, lang_for_user(user)))
     ).all()
 
     # Per-channel aggregates over the shared catalog in ONE grouped pass: stored count, last
@@ -139,7 +141,7 @@ def _discovery_rows(db: Session, user: User) -> list:
     return db.execute(
         q.group_by(Channel.id).order_by(
             func.count(func.distinct(PlaylistItem.video_id)).desc(),
-            func.lower(Channel.title),
+            collated(Channel.title, lang_for_user(user)),
         )
     ).all()
 
@@ -192,10 +194,14 @@ def discover_channels(
             ):
                 apply_channel_details(db, yt.get_channels(need), need)
             db.commit()
-            # Match _discovery_rows' ORDER BY exactly: video-count DESC, then title (NULLs LAST,
-            # as Postgres orders them — coercing NULL→"" would wrongly float untitled channels up).
+            # Match _discovery_rows' ORDER BY exactly: video-count DESC, then title in the reader's
+            # alphabet (NULLs LAST, as Postgres orders them — coercing NULL→"" would wrongly float
+            # untitled channels up).
+            titles = [r[0].title for r in rows if r[0].title is not None]
+            alpha = {w: i for i, w in enumerate(sorted_words(db, titles, lang_for_user(user)))}
             rows = sorted(
-                rows, key=lambda r: (-int(r[1]), r[0].title is None, (r[0].title or "").lower())
+                rows,
+                key=lambda r: (-int(r[1]), r[0].title is None, alpha.get(r[0].title or "", 0)),
             )
         except YouTubeError as exc:
             log.warning(
@@ -659,7 +665,7 @@ def list_blocked(user: User = Depends(current_user), db: Session = Depends(get_d
             select(Channel)
             .join(BlockedChannel, BlockedChannel.channel_id == Channel.id)
             .where(BlockedChannel.user_id == user.id)
-            .order_by(func.lower(Channel.title))
+            .order_by(collated(Channel.title, lang_for_user(user)))
         )
         .scalars()
         .all()