refactor: use configurable keybindings for all UI hints (#724)

Follow-up to #717. Replaces all remaining hardcoded keybinding hints with configurable ones.

- Add pasteImage to AppAction so it can be configured in keybindings.json
- Create keybinding-hints.ts with reusable helper functions:
  - editorKey(action) / appKey(keybindings, action) - get key display string
  - keyHint(action, desc) / appKeyHint(kb, action, desc) / rawKeyHint(key, desc) - styled hints
- Export helpers from components/index.ts for extensions
- Update all components to use configured keybindings
- Remove now-unused getDisplayString() from KeybindingsManager and EditorKeybindingsManager
- Use keybindings.matches() instead of matchesKey() for pasteImage in custom-editor.ts

packages/coding-agent/src/modes/interactive/components/branch-summary-message.ts

@@ -1,6 +1,7 @@
-import { Box, getEditorKeybindings, Markdown, Spacer, Text } from "@mariozechner/pi-tui";
+import { Box, Markdown, Spacer, Text } from "@mariozechner/pi-tui";
 import type { BranchSummaryMessage } from "../../../core/messages.js";
 import { getMarkdownTheme, theme } from "../theme/theme.js";
+import { editorKey } from "./keybinding-hints.js";
 
 /**
  * Component that renders a branch summary message with collapsed/expanded state.
@@ -41,11 +42,10 @@ export class BranchSummaryMessageComponent extends Box {
 				}),
 			);
 		} else {
-			const expandKey = getEditorKeybindings().getKeys("expandTools")[0]!;
 			this.addChild(
 				new Text(
 					theme.fg("customMessageText", "Branch summary (") +
-						theme.fg("dim", expandKey) +
+						theme.fg("dim", editorKey("expandTools")) +
 						theme.fg("customMessageText", " to expand)"),
 					0,
 					0,