feat: add Ghostty as a supported SSH/Telnet terminal on macOS

[Wisdom12333]

Summary

• Add a new built-in macOS plugin for Ghostty alongside the existing Terminal.app, iTerm2, and SecureCRT options under Settings → 应用配置 → 命令行连接 → SSH.
• Ghostty exposes no "do script" AppleEvent like Terminal.app/iTerm2, and driving it via open -na --args -e only cold-starts cleanly once — a second connection while it's already running triggers a native "Allow Ghostty to execute...?" confirmation and, if approved, opens a broken extra tab. The SSH launch path (go-client/pkg/awaken/awaken_darwin.go) instead drives Ghostty through its own AppleScript dictionary (new surface configuration / new tab in ... with configuration / new window with configuration), which works identically whether Ghostty is cold or already running, with no confirmation dialog.
• Repeat connections check the existing window count so they land as a new tab in the current window rather than opening a new window each time.
• Adds the plugin manifest/connect config/icon (plugins/macos/macos.ghostty/), registers it in plugins/macos/index.json, wires up the Settings UI icon, and updates README/README_CN/docs to mention Ghostty as a supported terminal.

Test plan

• go build ./... && go vet ./... && go test ./... in go-client — all pass
• cargo check --release in src-tauri — clean (only pre-existing, unrelated warnings)
• Manually built and ran the full .app locally (Tauri release build) and verified against a real JumpServer server:
  • Cold start: connecting via SSH opens exactly one Ghostty window with one tab, and the SSH session connects correctly (not a local shell)
  • Warm state: a second connection while Ghostty is already open adds a new tab to the same window, with no "Allow Ghostty to execute" dialog and no broken/duplicate tab
  • A failed/fast-exiting SSH command keeps the surface open (via "wait after command") instead of instantly closing

[Wisdom12333]