Teaching: hide-notes-until share, session length check, slides export

- A study share link can hide the owner's notes until a chosen time: the server
  sends only passages and discussion questions until then, with a banner in the
  shared view (new share_reveal column, migrated on start).
- Outline: a session length with "N of M min planned, X min over" and a marker
  on the point where the plan runs past it.
- Export > Slides: printable 16:9 slides (title, passage, outline points with
  their verse, discussion questions) for one session or all; light or dark.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/hooks/useShareLink.js

@@ -6,14 +6,15 @@ export function useShareLink(projectId) {
   const [shareToken, setShareToken] = useState(null);
   const [expiresAt, setExpiresAt] = useState(null);
   const [hasPasscode, setHasPasscode] = useState(false);
+  const [revealAt, setRevealAt] = useState(null);
   const [shareBusy, setShareBusy] = useState(false);
   const [shareCopied, setShareCopied] = useState(false);
   const [shareError, setShareError] = useState('');
 
-  const apply = (data) => { setShareToken(data.shareToken ?? null); setExpiresAt(data.expiresAt ?? null); setHasPasscode(!!data.hasPasscode); };
+  const apply = (data) => { setShareToken(data.shareToken ?? null); setExpiresAt(data.expiresAt ?? null); setHasPasscode(!!data.hasPasscode); setRevealAt(data.revealAt ?? null); };
 
   useEffect(() => {
-    setShareToken(null); setExpiresAt(null); setHasPasscode(false); setShareError('');
+    setShareToken(null); setExpiresAt(null); setHasPasscode(false); setRevealAt(null); setShareError('');
     if (!projectId) return undefined;
     let active = true;
     getShareStatus(projectId).then((result) => {
@@ -26,7 +27,7 @@ export function useShareLink(projectId) {
     ? `${window.location.origin}${window.location.pathname}?share=${shareToken}`
     : '';
 
-  // Turns the link on, or changes its rules: { expiresInDays?: number | null, passcode?: string | null }
+  // Turns the link on, or changes its rules: { expiresInDays?: number | null, passcode?: string | null, revealAt?: number | null }
   const enable = async (options = {}) => {
     setShareBusy(true);
     setShareError('');
@@ -52,5 +53,5 @@ export function useShareLink(projectId) {
     });
   };
 
-  return { shareToken, shareUrl, expiresAt, hasPasscode, shareBusy, shareCopied, shareError, enable, revoke, copy };
+  return { shareToken, shareUrl, expiresAt, hasPasscode, revealAt, shareBusy, shareCopied, shareError, enable, revoke, copy };
 }