feat(web): split the home page into quick share and spaces zones

Two side-by-side zones (stacked on narrow screens) with an icon and a
one-line positioning each: quick share is temporary, read-only and needs
no account; spaces are long-lived, multi-user and need a login. Shorter
copy, my shares listed under the share input, and an empty state for
spaces.

web/src/features/home/ChannelList.tsx

@@ -11,9 +11,11 @@ interface Props {
   kind: 'channel' | 'share';
   title: string;
   onOpen: (c: ChannelInfo | Share) => void;
+  /** 标题只给屏幕阅读器(所在分区已有标题) */
+  quietTitle?: boolean;
 }
 
-export function ChannelList({ kind, title, onOpen }: Props) {
+export function ChannelList({ kind, title, onOpen, quietTitle = false }: Props) {
   const channels = useChannels((s) => s.list);
   const forgetChannel = useChannels((s) => s.forget);
   const shares = useShares((s) => s.list);
@@ -24,7 +26,7 @@ export function ChannelList({ kind, title, onOpen }: Props) {
 
   return (
     <section aria-label={title}>
-      <h2 className={styles.h}>{title}</h2>
+      <h2 className={`${styles.h} ${quietTitle ? styles.quiet : ''}`}>{title}</h2>
       <ul className={styles.list}>
         {list.map((c) => (
           <li key={c.id} className={styles.row}>