docs: reconcile screen-layout docs with the panel changes

Mode now sits at the side panel's bottom-left (not its top), and the
words-this-session field is gone. Update the CONTEXT.md field list and
the product-doc mock + prose to match; note the keyboard flag renders
as NO KBD (Latin-9 has no glyph for the mock's symbols).

CONTEXT.md

@@ -67,8 +67,9 @@ full-width text region before the side panel carved out its right edge).
 
 **Side panel**:
 The right region (~150 px / ~20 cols, full height) holding all metadata:
-filename + dirty dot, mode, word count, session, clock, Wi-Fi,
-keyboard-disconnect flag, publish state. Sits entirely in the master half
+filename + dirty dot, word count, elapsed time, clock, Wi-Fi,
+keyboard-disconnect flag, publish state, and the mode indicator at its
+bottom-left. Sits entirely in the master half
 (right of the `x = 396` seam). Every field is static, event-driven, or
 throttled — never per-keystroke.
 _Avoid_: header, status line, status bar (retired — the old top header band and