feat(update): add rolling dev update channel for per-commit builds

Adds an opt-in Dev channel so panels running CI per-commit builds can self-update to the latest commit, mirroring the stable online-update flow.

CI publishes/overwrites a single fixed-tag pre-release (dev-latest), force-moved to the newest main commit and marked --latest=false so releases/latest stays the stable tag. Builds stamp the short commit via -ldflags; the panel compares the running commit to the dev release commit to detect an update, and update.sh honors XUI_UPDATE_TAG to install from that tag. Linux/systemd only.

internal/web/translation/zh-CN.json

@@ -153,6 +153,11 @@
       "currentPanelVersion": "当前面板版本",
       "latestPanelVersion": "最新面板版本",
       "panelUpToDate": "面板已是最新",
+      "devChannel": "开发通道",
+      "devChannelWarning": "开发版会跟踪 main 的每次提交，并非稳定版本，且无法自动降级。",
+      "currentCommit": "当前提交",
+      "latestCommit": "最新提交",
+      "updateChannelChanged": "更新通道已切换",
       "upToDate": "已是最新",
       "xrayStatusUnknown": "未知",
       "xrayStatusRunning": "运行中",