Transcript mode: f, d, u bare keys missing from otherwise less-compatible keybinding set

Summary

Transcript mode (ctrl+o) already adopts less/pager-style bare-key navigation for most common operations, but f, d, and u are missing.

Current state

Transcript mode supports these less-style bare keys:

| Key | Action | Status |
|-----|--------|--------|
| Space | Forward one page | ✅ Works |
| b | Back one page | ✅ Works |
| g | Go to top | ✅ Works |
| G | Go to bottom | ✅ Works |
| q | Quit | ✅ Works |
| f | Forward one page | ❌ Missing |
| d | Forward half page | ❌ Missing |
| u | Back half page | ❌ Missing |

ctrl+d / ctrl+u already work for half-page scrolling, so the underlying scroll actions exist — d and u would just be bare-key aliases, consistent with how b is already a bare-key alias for ctrl+b.

Rationale

Transcript mode is a read-only viewer with no editing capabilities, so bare d, u, and f have no conflicting purpose. The mode has clearly adopted a pager (less) keybinding model — 5 out of 8 common less navigation keys already work. Adding the remaining 3 is a straightforward consistency fix.