- FeedResponse claimed a required `limit`, but /api/search/youtube never
returns it (only /api/feed does) and nothing in the app reads it. Drop the
field so searchYoutube's Promise<FeedResponse> stops lying; documented for
re-add if a consumer appears.
- pageMeta's hand-written 13-case Page->title switch now derives from the
ModuleDef registry via a new optional `titleKey` (the longer tab title, e.g.
"Channel manager"; falls back to the short nav labelKey). A new page is one
touch (add it to MODULES) instead of also editing a switch. A test pins all
13 title keys byte-identical to the old switch (suite 74).