refactor(plugins): remove auto-jimaku example plugin and fix docs

- Remove the auto-jimaku example, now covered by the built-in Jimaku auto-open
- Drop its plugins docs section and changelog bullet
- List the keyboard-only `C` key in Keyboard shortcuts
- Point the configuration reference to Controller support for button defaults

changes/docs-keyboard-character-navigation.md

@@ -0,0 +1,4 @@
+type: docs
+area: overlay
+
+- Listed the keyboard-only `C` key in Keyboard shortcuts, and pointed the configuration reference to Controller support for default button actions.