DLP on send: warnings, blocks and held mail in the composer

The webmail half of inbuxa's DLP (dlp-and-mail-flow-rules spec, §2.5,
§4):

- A send the server's DLP rules refuse (inbuxa:dlpWarning or
  inbuxa:dlpBlocked) comes back to the composer with the rules' notices
  instead of a generic "Send failed". A warning offers "Send anyway…",
  which asks for a reason and sends again with inbuxa:dlpOverride; the
  server records the reason. A block can only be answered by changing
  the message.
- A message DLP held for review says so on sending ("Held for review:
  it's sent once a reviewer releases it"), from the submission's
  inbuxa:held.
- Tests: the override travels with the submission only when there's a
  reason; refusals are told apart from other errors.

Nine new English strings (the notice labels, the prompt, the toasts);
the other catalogs fall back to English until translated.

web/src/store/__tests__/compose-dlp.test.ts

@@ -0,0 +1,39 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+// inbuxa: DLP on send: the override travels with the submission, and the
+// server's refusals are told apart from other errors.
+import { describe, expect, it } from "vitest";
+import { buildSubmission, dlpRefusalOf } from "../compose";
+
+const base = {
+  identityId: "i1",
+  fromEmail: "[email protected]",
+  emailRef: "#m",
+  rcpts: [{ email: "[email protected]" }],
+  sentId: "sent",
+  draftsId: "drafts",
+  scheduledId: null,
+  sendAt: null,
+};
+
+describe("DLP on send", () => {
+  it("sends the override reason only when there is one", () => {
+    expect(buildSubmission(base).create["inbuxa:dlpOverride"]).toBeUndefined();
+    expect(buildSubmission({ ...base, dlpOverride: "  " }).create["inbuxa:dlpOverride"]).toBeUndefined();
+    expect(buildSubmission({ ...base, dlpOverride: " Client asked " }).create["inbuxa:dlpOverride"]).toEqual({ reason: "Client asked" });
+  });
+
+  it("recognizes the server's refusals", () => {
+    expect(dlpRefusalOf({ type: "inbuxa:dlpWarning", rules: [{ name: "Cards", notice: "Looks like a card." }] })).toEqual({
+      kind: "warning",
+      rules: [{ name: "Cards", notice: "Looks like a card." }],
+    });
+    expect(dlpRefusalOf({ type: "inbuxa:dlpBlocked" })).toEqual({ kind: "blocked", rules: [] });
+    expect(dlpRefusalOf({ type: "forbiddenToSend" })).toBeNull();
+    expect(dlpRefusalOf(undefined)).toBeNull();
+  });
+});