feat(channels): leading '＋ Tag' pill + detail-page Unhide affordance (S6)

Item 6 — the tag add-trigger now LEADS the chip row (a stable left anchor)
instead of trailing it, so on the detail page (bounded=false) adding chips
grows the row to its right and the '+'/its editor popover no longer drift.
Compact icon in the width-bounded manager cell; a labelled '＋ Tag' pill
where there's free width (the detail header).

Item 7 — surface the per-subscription 'hidden' flag on the detail GET
(channel_detail was omitting it) and add an Eye/EyeOff hide/unhide toggle
next to Block on the channel page, mirroring the manager. FE ChannelDetail
gains 'hidden'; new channel.* i18n keys (HU+EN).

Tests: +3 backend (channel_detail surfaces hidden, both states + unsubscribed
default). Gate green: backend pytest 471, FE vitest 498.

backend/app/routes/channels.py

@@ -229,6 +229,7 @@ def _channel_detail_dict(
     count_live: int,
     deep_requested: bool,
     priority: int,
+    hidden: bool,
     tag_ids: list[int],
 ) -> dict:
     return {
@@ -262,6 +263,9 @@ def _channel_detail_dict(
         # This user's per-subscription feed priority (0 when not subscribed) so the channel page can
         # offer the same priority stepper as the manager. Editable only while subscribed.
         "priority": priority,
+        # This user's per-subscription "hide from feed" flag (False when not subscribed), so the
+        # channel page can offer the same Unhide toggle the manager has. Editable only while subscribed.
+        "hidden": hidden,
         "backfill_done": channel.backfill_done,
         "from_explore": channel.from_explore,
         "details_synced": channel.details_synced_at is not None,
@@ -344,6 +348,7 @@ def channel_detail(
         count_live=count_live,
         deep_requested=bool(sub.deep_requested) if sub else False,
         priority=int(sub.priority) if sub else 0,
+        hidden=bool(sub.hidden) if sub else False,
         tag_ids=tag_ids,
     )