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/config/config.go

@@ -20,6 +20,15 @@ var version string
 //go:embed name
 var name string
 
+// buildCommit and buildDate are injected at build time via `-ldflags -X` for
+// CI per-commit (dev channel) builds; see .github/workflows/release.yml. They
+// stay empty for a plain `go build` and for stable tagged releases, which is how
+// IsDevBuild tells a rolling dev build apart from a stable/local one.
+var (
+	buildCommit string
+	buildDate   string
+)
+
 // LogLevel represents the logging level for the application.
 type LogLevel string
 
@@ -42,6 +51,23 @@ func GetName() string {
 	return strings.TrimSpace(name)
 }
 
+// GetBuildCommit returns the short git commit this binary was built from, or an
+// empty string for a plain/local build or a stable tagged release.
+func GetBuildCommit() string {
+	return strings.TrimSpace(buildCommit)
+}
+
+// GetBuildDate returns the UTC build timestamp injected at build time, or empty.
+func GetBuildDate() string {
+	return strings.TrimSpace(buildDate)
+}
+
+// IsDevBuild reports whether this binary is a CI per-commit (dev channel) build,
+// detected by the injected commit. Stable releases and local builds return false.
+func IsDevBuild() bool {
+	return GetBuildCommit() != ""
+}
+
 // GetLogLevel returns the current logging level based on environment variables or defaults to Info.
 func GetLogLevel() LogLevel {
 	if IsDebug() {