Expand discovery pool and remove header logo

Double search results per query (20→40), increase query budget (15→25),
use more tags per signal (6→10-12), index more new channels per refresh
(5→10). Remove the YT logo from the header.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Layout.jsx

@@ -1,4 +1,4 @@
-import { Outlet, NavLink, useNavigate, Link, useLocation } from "react-router-dom";
+import { Outlet, NavLink, Link, useLocation } from "react-router-dom";
 import { useQuery } from "@tanstack/react-query";
 import { useAuth } from "../hooks/useAuth";
 import SearchBar from "./SearchBar";
@@ -203,7 +203,6 @@ function useNewVideosCount() {
 
 export default function Layout() {
   const { user, logout } = useAuth();
-  const navigate = useNavigate();
   const newCount = useNewVideosCount();
 
   return (
@@ -211,14 +210,6 @@ export default function Layout() {
       {/* Header */}
       <header className="shrink-0 z-40 bg-zinc-950/90 backdrop-blur border-b border-zinc-800">
         <div className="max-w-screen-xl mx-auto px-3 h-12 sm:h-14 flex items-center gap-2 sm:gap-4">
-          {/* Logo */}
-          <button
-            onClick={() => navigate("/")}
-            className="font-display font-bold text-base sm:text-lg text-zinc-100 shrink-0 tracking-tight"
-          >
-            YT
-          </button>
-
           {/* Search — min-w-0 prevents it from overflowing on narrow screens */}
           <div className="flex-1 min-w-0">
             <SearchBar />