docs(tui): document shifted-letter keybinding compatibility

Clarify that shifted letter bindings are matched compatibly when
terminals emit uppercase letters without an explicit SHIFT modifier.

Update config guidance, the default keymap template, and the action
matrix with examples for shift-i, shift-a, and shift-o mapping to I, A,
and O.

docs/config.md

@@ -95,7 +95,9 @@ Actions accept a single key or multiple keys:
 Some defaults intentionally include multiple variants for one logical shortcut
 because terminal modifier reporting can differ by platform/emulator. For
 example, `?` may arrive as plain `?` or `shift-?`, and control chords may
-arrive with or without `SHIFT`.
+arrive with or without `SHIFT`. Shifted letter bindings are also matched
+compatibly when terminals report uppercase letters without explicit `SHIFT`
+(for example, `shift-i` matching `I`).
 
 Aliases like `escape`, `pageup`, and `pgdn` are normalized.
 

docs/default-keymap.toml

@@ -73,6 +73,8 @@ yank = ["ctrl-y"]
 
 [tui.keymap.vim_normal]
 # Vim normal-mode actions for modal editing.
+# Shifted letter bindings also match uppercase event forms reported without
+# explicit SHIFT by some terminals.
 enter_insert = "i"
 append_after_cursor = "a"
 append_line_end = "shift-a"

docs/keymap-action-matrix.md

@@ -24,6 +24,9 @@ For runtime behavior, safety invariants, and testing guidance, see
   - `composer.toggle_shortcuts`: `?` and `shift-?`
   - `approval.open_fullscreen`: `ctrl-a` and `ctrl-shift-a`
   - `onboarding.toggle_animation`: `ctrl-.` and `ctrl-shift-.`
+- Shifted letter bindings are also matched compatibly across terminal variants
+  when reported as uppercase letters without explicit `SHIFT` (for example
+  `shift-i` matching `I`, `shift-a` matching `A`, and `shift-o` matching `O`).
 - Keep these paired defaults unless/until key-event normalization is made
   platform-consistent at a lower layer.