fix(chat): forward polish + scrollbar + image preview + media tabs

- #4: forward modal buttons now branded (bzc-* un-scoped from .bz-confirm); target
  rows get real checkboxes + border highlight; selected MESSAGES highlight in green
  with a filled tick (distinct from blue bubbles), checkbox on every message.
- #5: forwarded messages show an italic 'Forwarded from <origin>' label; new fwd_from
  column preserves the true origin across re-forwards.
- #6: image-preview arrows are smaller (32px) chevron icons, clear of the image
  (image max 82vw); icons.js?v=5.
- #10: image preview now opens ABOVE the media modal (z 9900) and Esc/close returns
  to the media view instead of closing everything.
- #11: Media/Links/Docs active tab underline is brand-blue, not green.
- #2: chat-list + conversation scrollbars 6px, stepper arrows hidden; pagination adds
  a cooldown + overflow-anchor:none so scrolling up no longer sticks/jumps.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/db.js

@@ -218,6 +218,7 @@ try { db.exec('ALTER TABLE messages ADD COLUMN msg_type TEXT'); } catch (e) { /*
 try { db.exec('ALTER TABLE messages ADD COLUMN deleted INTEGER NOT NULL DEFAULT 0'); } catch (e) { /* exists */ }
 // A message can be edited by its sender; edited_at marks it (shows an "edited" label).
 try { db.exec('ALTER TABLE messages ADD COLUMN edited_at INTEGER'); } catch (e) { /* exists */ }
+try { db.exec('ALTER TABLE messages ADD COLUMN fwd_from TEXT'); } catch (e) { /* exists — original sender name when a message was forwarded (#5) */ }
 // User-set presence status: 'active' | 'away' | 'onleave'. ('incall' is derived live, not stored.)
 try { db.exec("ALTER TABLE users ADD COLUMN status TEXT NOT NULL DEFAULT 'active'"); } catch (e) { /* exists */ }
 // BizGaze person-id (s.userId): the SAME value whether the person signs in with their email or