fix(notifications): a confirm names its user and channel again; t() and a notice's text are kept apart by a contract

The value sweep wrapped two plain t() values in raw(), so the delete-user and the YouTube subscribe
confirms read "[object Object]" where the email or the channel was. tsc cannot see that seam, so a
syntax contract now refuses a notice value handed to t() and an already-said text kept in a notice.
The raw() doc says what it is: text kept as fetched (a Plex title in the language it was fetched in).
seasonTitleText's no-number branches are tested.

frontend/src/lib/notifText.contract.test.ts

@@ -0,0 +1,73 @@
+import { describe, expect, it } from "vitest";
+import ts from "typescript";
+import { readSources } from "./rawSources.testkit";
+
+// A notice says WHAT to say (lib/notifications NotifText) and is said when shown; a plain `t()` says
+// it now. tsc cannot tell the two apart where they meet — `msg`'s key is a string, `detail` is
+// unknown, and i18next's options take any value — so the slips are caught here, on the syntax:
+// - a NotifText handed to `t()` as a value (`t("k", { name: raw(x) })`) reads "[object Object]";
+// - an already-said text kept in a notice (`msg(t("k"))`, `raw(t("k"))`, `{ detail: t("k") }`)
+//   stays in the language it was raised in.
+
+const isT = (e: ts.Expression) =>
+  (ts.isIdentifier(e) && e.text === "t") ||
+  (ts.isPropertyAccessExpression(e) && e.name.text === "t");
+const isCallTo = (e: ts.Node, names: string[]): e is ts.CallExpression =>
+  ts.isCallExpression(e) && ts.isIdentifier(e.expression) && names.includes(e.expression.text);
+const isTCall = (e: ts.Node): e is ts.CallExpression => ts.isCallExpression(e) && isT(e.expression);
+
+function mixedNotifText(name: string, src: string): string[] {
+  const file = ts.createSourceFile(name, src, ts.ScriptTarget.Latest, true, ts.ScriptKind.TSX);
+  const out: string[] = [];
+  const at = (n: ts.Node, what: string) =>
+    out.push(`${name}:${file.getLineAndCharacterOfPosition(n.getStart()).line + 1} ${what}`);
+  const visit = (n: ts.Node) => {
+    if (isTCall(n)) {
+      for (const arg of n.arguments.slice(1)) {
+        if (!ts.isObjectLiteralExpression(arg)) continue;
+        for (const p of arg.properties) {
+          if (ts.isPropertyAssignment(p) && isCallTo(p.initializer, ["raw", "msg"]))
+            at(p, "a notice value handed to t()");
+        }
+      }
+    }
+    if (isCallTo(n, ["msg", "raw"]) && n.arguments[0] && isTCall(n.arguments[0]))
+      at(n, "a said text kept in a notice");
+    if (
+      ts.isPropertyAssignment(n) &&
+      ts.isIdentifier(n.name) &&
+      n.name.text === "detail" &&
+      isTCall(n.initializer)
+    )
+      at(n, "a said text kept as a notice's detail");
+    ts.forEachChild(n, visit);
+  };
+  visit(file);
+  return out;
+}
+
+describe("a notice's text and a plain t() do not mix", () => {
+  it("holds across src", () => {
+    const files = readSources(__dirname, ["../**/*.ts", "../**/*.tsx", "!../**/*.test.*"]);
+    expect(Object.keys(files).length).toBeGreaterThan(100); // the glob matched the app
+    expect(Object.entries(files).flatMap(([p, src]) => mixedNotifText(p, src))).toEqual([]);
+  });
+
+  it.each([
+    ['t("users.delete.confirm", { email: raw(u.email) })', "a notice value handed to t()"],
+    ['i18n.t("k", { n: msg("x") })', "a notice value handed to t()"],
+    ['notify({ message: msg(t("feed.saved")) })', "a said text kept in a notice"],
+    ['notify({ message: raw(t("feed.saved")) })', "a said text kept in a notice"],
+    ['notify({ message: { detail: t("x") } })', "a said text kept as a notice's detail"],
+  ])("sees %s", (src, what) => {
+    expect(mixedNotifText("x.tsx", src)).toEqual([`x.tsx:1 ${what}`]);
+  });
+
+  it.each([
+    'msg("channels.discovery.subscribedBody", { name: raw(nameOf(c)) })',
+    't("channels.discovery.confirmSubscribe", { name: nameOf(c) })',
+    "sayNotif(msg(key), t)",
+  ])("lets %s through", (src) => {
+    expect(mixedNotifText("x.tsx", src)).toEqual([]);
+  });
+});