feat: support command: prefix in keymap actions

[WayneKent]

Summary

Add command: prefix support to keymap actions. Users can now bind arbitrary opencode commands via the vim plugin keymaps.

Usage

"keymaps": {
  "normal": {
    "<C-k>": "command:prompt.history.previous",
    "<C-j>": "command:prompt.history.next"
  },
  "insert": {
    "<C-k>": "command:prompt.history.previous",
    "<C-j>": "command:prompt.history.next"
  }
}

Available commands can be found in opencode source: packages/tui/src/component/prompt/index.tsx and packages/tui/src/config/keybind.ts.

Notes

• For prompt.history.previous and prompt.history.next, the vim plugin automatically moves the cursor to the start/end before dispatching. If you prefer the default opencode behavior (cursor must already be at the start/end, otherwise first press only moves cursor), configure these keybinds in opencode's own keybinds config instead of the vim plugin's keymaps.
• English configuration.md and Chinese documentation will be updated once PR feat: <CR> respects mode-specific keymaps #14 (feat/cr-mode-aware) is merged. This PR contains only the implementation.