refactor(cli): extract vim prompt logic into kilocode mirror

Move the vim modal editing engine and prompt integration out of shared
upstream files and into src/kilocode/ mirrors per the Fork Isolation Rule:

- src/kilocode/cli/cmd/tui/component/prompt/vim.ts (engine, moved)
- src/kilocode/cli/cmd/tui/component/prompt/index.tsx (new mirror with
  useVim, VimModeIndicator, vimToggleCommand)
- test/kilocode/cli/cmd/tui/prompt/vim.test.ts (moved)

The shared prompt/index.tsx now calls into the mirror behind minimal
kilocode_change markers instead of inlining ~200 lines of vim logic.

packages/opencode/test/kilocode/cli/cmd/tui/prompt/vim.test.ts

@@ -9,7 +9,7 @@ import {
   clampNormal,
   type VimDoc,
   type VimKey,
-} from "@tui/component/prompt/vim"
+} from "@/kilocode/cli/cmd/tui/component/prompt/vim"
 
 /** In-memory document implementing the engine's VimDoc contract. */
 class MockDoc implements VimDoc {