feat: let subscriptions be renamed from the list (#1044)

A subscription's name is captured once at subscribe time from the feed's own
title, so playlists — particularly the UULF-prefixed channel-uploads playlists
— all come back named "Videos" and stay that way. Adds an inline editor on the
Name cell, mirroring the existing title-filter edit next to it.

The update route already whitelisted `name` and update_subscription already
applied it, so this is mostly the missing UI. The backend side is validation:
the old `str(changes["name"])` accepted any type, any length and any
whitespace, for a value that is persisted and broadcast to every connected
client. validate_subscription_name now requires a string, collapses interior
whitespace to keep the label single-line, and caps it at 200 characters.

The name is display-only — it is used for the subscription list and log lines,
never for download paths — so renaming cannot move where files land.

ui/src/app/app.ts

@@ -102,6 +102,9 @@ export class App implements AfterViewInit, OnInit, OnDestroy {
   skipSubscriberOnly = false;
   editingTitleRegexId: string | null = null;
   titleRegexEditDraft = '';
+  editingNameId: string | null = null;
+  nameEditDraft = '';
+  readonly subscriptionNameMaxLength = 200;
   cachedSubs: [string, SubscriptionRow][] = [];
   selectedSubscriptionIds = new Set<string>();
   checkingSubscriptionIds = new Set<string>();
@@ -663,6 +666,34 @@ export class App implements AfterViewInit, OnInit, OnDestroy {
     });
   }
 
+  beginEditName(id: string, current: string | undefined) {
+    this.editingNameId = id;
+    this.nameEditDraft = current ?? '';
+    this.cdr.markForCheck();
+  }
+
+  cancelEditName() {
+    this.editingNameId = null;
+    this.nameEditDraft = '';
+    this.cdr.markForCheck();
+  }
+
+  saveName(id: string) {
+    const name = (this.nameEditDraft || '').trim();
+    if (!name) {
+      this.toasts.error('Subscription name must not be empty');
+      return;
+    }
+    this.subscriptionsSvc.update(id, { name }).subscribe((res) => {
+      const error = this.getStatusError(res);
+      if (error) {
+        this.toasts.error(error || 'Update subscription failed');
+        return;
+      }
+      this.cancelEditName();
+    });
+  }
+
   deleteSubscription(id: string) {
     this.subscriptionsSvc.delete([id]).subscribe((res) => {
       const error = this.getStatusError(res);