Implement milestone M2b of the MCP remote-control design: inject keyboard
events through an existing screen sub-connection.
- Extract the MSG64 keyboard construction from WebService::HandleKey into a
shared inline BuildKeyMsg64 helper in WebService.h, and have HandleKey use
it (behaviour-preserving) so the Web and MCP paths cannot drift.
- Add BuildRemoteKeyboard with four actions: key_down / key_up / key_press
(key name -> VK via MapKeyNameToVk, plus CTRL/ALT/SHIFT/WIN modifiers) and
type (per-character VkKeyScanA mapping, ASCII only, newline/tab -> Enter/Tab).
The batch is sent as one [COMMAND_SCREEN_CONTROL][MSG64*N] packet over the
screen sub-connection under the existing Begin/EndScreenCtrlAction busy
discipline, then audited via WM_SHOWERRORMSG.
Non-ASCII text is rejected (-32602) and must go through remote_clipboard +
Ctrl+V (milestone M4), matching the design's clipboard path for CJK input.
Co-Authored-By: deepseek-v4-pro
f04d892ac8