Add cross-platform serial tool support (#2673)

* feat(tools): add cross-platform serial hardware tool

* feat(config): wire serial tool into runtime and dashboard

* hardware/serial: tighten validation and error handling

* hardware/serial: improve unix cancellation and timeout polling

* hardware/serial: improve windows I/O handling

* hardware/serial: fix darwin cross-compilation build

* docs(design): summarize hardware support and serial limits

* build: keep go generate on host during cross builds

* onboard: drop unrelated go generate change from serial work

* style(tools): wrap serial lines for golines

web/frontend/src/i18n/locales/en.json

@@ -603,6 +603,7 @@
         },
         "reasons": {
           "requires_linux": "This tool only works on Linux hosts with the required device files exposed.",
+          "requires_serial_platform": "This tool currently supports Linux, macOS, and Windows hosts with accessible serial ports.",
           "requires_skills": "Enable `tools.skills` before this skill-registry tool can be used.",
           "requires_subagent": "Enable `tools.subagent` before the spawn tool can delegate work.",
           "requires_mcp_discovery": "Enable `tools.mcp.discovery` before MCP discovery tools become available.",

web/frontend/src/i18n/locales/zh.json

@@ -603,6 +603,7 @@
         },
         "reasons": {
           "requires_linux": "该工具仅在 Linux 主机上可用，并且需要暴露对应的设备文件。",
+          "requires_serial_platform": "该工具当前支持 Linux、macOS 和 Windows，且要求主机可访问对应串口。",
           "requires_skills": "需要先启用 `tools.skills`，该技能注册表工具才能使用。",
           "requires_subagent": "需要先启用 `tools.subagent`，`spawn` 才能委派任务。",
           "requires_mcp_discovery": "需要先启用 `tools.mcp.discovery`，MCP 发现工具才会可用。",