Generalize podcast-specific UI for study-only users

Other people using this app just want to do personal Bible study, not
produce a podcast episode, so the always-visible chrome (chunk
metadata, DOCX import, exports) now says "Session" instead of
"Episode" and marks podcast-only fields as optional. The "Prepare for
Podcast" prompt no longer hardcodes "Verse by Verse with Nate" for
every user — it now pulls from a new "Podcast / show name" field in
Account Settings, so it still works exactly as before once you set
yours, but produces a sensible generic prompt for anyone who hasn't.
Also added an explanatory blurb to the session-list import page and
loosened its docx parser to accept "Session N — Title" in addition to
"Ep. N — Title".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/syncService.js

@@ -111,6 +111,11 @@ export async function verifyMfaLogin({ token, backupCode }) {
   return request('POST', '/auth/mfa/verify', { token, backupCode });
 }
 
+/** Updates account-level profile settings (currently just the podcast/show name). */
+export async function updateProfile({ podcastName }) {
+  return request('PATCH', '/auth/profile', { podcastName });
+}
+
 // ---------------------------------------------------------------------------
 // Two-factor auth setup (Account Settings page)
 // ---------------------------------------------------------------------------