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.

frontend/src/components/ChannelPage.tsx

@@ -12,6 +12,8 @@ import {
   Ban,
   Check,
   ExternalLink,
+  Eye,
+  EyeOff,
   History,
   Loader2,
   Plus,
@@ -137,6 +139,17 @@ export default function ChannelPage({
     // a caller toast here would just double it.
   });
 
+  // "Hide from feed": the same per-subscription flag the manager toggles (updateChannel {hidden}).
+  // Local DB op — keeps the subscription, only drops the channel's videos from the feed/explore.
+  const toggleHidden = useMutation({
+    mutationFn: () => api.updateChannel(channelId, { hidden: !ch?.hidden }),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: qk.channel(channelId) });
+      qc.invalidateQueries({ queryKey: qk.feed() });
+      qc.invalidateQueries({ queryKey: qk.channels() });
+    },
+  });
+
   const subscribe = useMutation({
     mutationFn: () => api.subscribeChannel(channelId),
     onSuccess: () => {
@@ -470,6 +483,24 @@ export default function ChannelPage({
                   <Ban className="w-4 h-4" />
                 </button>
               )}
+              {/* Hide-from-feed toggle — subscription-scoped, so offered only on a followed channel
+                  (mirrors the manager's Eye/EyeOff). Keeps the subscription; only drops its videos
+                  from the feed. EyeOff = currently hidden (click to unhide). */}
+              {ch?.subscribed && !me.is_demo && (
+                <button
+                  onClick={() => toggleHidden.mutate()}
+                  disabled={toggleHidden.isPending}
+                  title={ch.hidden ? t("channel.hiddenHint") : t("channel.hideHint")}
+                  aria-label={ch.hidden ? t("channel.unhide") : t("channel.hide")}
+                  className={`inline-flex items-center justify-center w-9 h-9 rounded-lg border disabled:opacity-50 transition ${
+                    ch.hidden
+                      ? "border-accent text-accent"
+                      : "border-border text-muted hover:text-fg hover:border-fg/40"
+                  }`}
+                >
+                  {ch.hidden ? <EyeOff className="w-4 h-4" /> : <Eye className="w-4 h-4" />}
+                </button>
+              )}
               {!me.is_demo &&
                 !ch?.blocked &&
                 (ch?.subscribed ? (