fix: T6 browser-check findings (compliance, treatments, labels)

- api-client accepts 2xx answers without body (revoke showed an error)
- authority notices: sentOn in the future is rejected (Berlin day) on
  create, mark-sent and PATCH; dialog defaults to the Berlin day
- service worker never caches /api/v1/site-settings
- treatments/new no longer overflows at 390 px (min-w-0 on form
  wrappers); dose with more than 3 decimals is an error, never rounded
- medicines: expired lots flagged, disposal over the rest warns
- label designer: side panel at lg, sample values instead of
  placeholders, compliance panel reopens on lg, labelled zoom buttons
- skip link to #main-content, headings on no-access pages

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Frontend/src/lib/auth/api-client.spec.ts

@@ -44,6 +44,33 @@ describe("api-client", () => {
     expect((apiError.body as { invalidColonyIds: string[] }).invalidColonyIds).toEqual(["c1"]);
   });
 
+  describe("empty success bodies", () => {
+    it.each([200, 201, 202])("resolves undefined for a %i with an empty body", async (status) => {
+      vi.stubGlobal("fetch", vi.fn().mockResolvedValue(new Response("", { status })));
+      await expect(apiFetch("/x", { method: "POST" })).resolves.toBeUndefined();
+    });
+
+    it("resolves undefined for a 204", async () => {
+      vi.stubGlobal("fetch", vi.fn().mockResolvedValue(new Response(null, { status: 204 })));
+      await expect(apiFetch("/x", { method: "POST" })).resolves.toBeUndefined();
+    });
+
+    it("resolves undefined when Content-Length is 0", async () => {
+      vi.stubGlobal(
+        "fetch",
+        vi.fn().mockResolvedValue(new Response("", { status: 201, headers: { "Content-Length": "0" } })),
+      );
+      await expect(apiFetch("/x", { method: "POST" })).resolves.toBeUndefined();
+    });
+
+    it("still parses a JSON body and still rejects invalid JSON", async () => {
+      vi.stubGlobal("fetch", vi.fn().mockResolvedValue(jsonResponse(201, { id: "a" })));
+      await expect(apiFetch("/x", { method: "POST" })).resolves.toEqual({ id: "a" });
+      vi.stubGlobal("fetch", vi.fn().mockResolvedValue(new Response("<html>", { status: 200 })));
+      await expect(apiFetch("/x")).rejects.toBeInstanceOf(SyntaxError);
+    });
+  });
+
   it("reports network-error on a failed fetch and reached-server on any HTTP answer", async () => {
     vi.stubGlobal("fetch", vi.fn().mockRejectedValue(new TypeError("Failed to fetch")));
     await expect(apiFetch("/x")).rejects.toBeInstanceOf(TypeError);