feat: harden support, localize knowledge and add operator availability [skip ci]

Source-only publication of reviewed commit 64e96a7f423673dc29ad56485be9fc79bce8af1c.

Passed in isolation: focused frontend/backend tests, race checks, TypeScript typecheck, lint, Go compilation, Flowgram build, and deterministic SDK build/tests.

Not accepted as a production release: Next.js export/native assembly remains blocked by environment memory limits; browser interaction and MySQL staging acceptance remain unverified. No production server, database/schema, runtime configuration, deployment, release tag, or workflow execution was performed.

Expected source tree: 0a4a7528e9.

internal/handlers/api/support_status_handler.go

@@ -0,0 +1,22 @@
+package api
+
+import (
+	"agent-desk/internal/pkg/httpx"
+	"agent-desk/internal/services"
+	"github.com/gin-gonic/gin"
+)
+
+func SupportGetStatus(ctx *gin.Context) {
+	channel := services.ChannelService.GetEnabledChannel(ctx)
+	if channel == nil {
+		httpx.WriteJSON(ctx, httpx.JsonErrorMsg(ctx, "error.e0209"))
+		return
+	}
+	result, err := services.SupportAvailabilityService.PublicStatus(channel)
+	if err != nil {
+		httpx.WriteJSON(ctx, err)
+		return
+	}
+	ctx.Header("Cache-Control", "no-store")
+	httpx.WriteJSON(ctx, result)
+}