feat(i18n): every server refusal is said by a record the contract holds

A refusal code or reason with no sentence fell through to the generic
"couldn't carry out that action" unnoticed: the parity test is green when
EN and HU miss the same key. One did (an edit refused for a file that is
not video or audio).

- lib/api/refusalCodes.ts: which sentence answers each code, as data;
  localizeDetail says a refusal through it, unchanged for every reader.
- backendIds contract: every detail code the backend sends is in exactly
  one record, every reason it can carry has its sentence in EN and HU,
  and no family names a reason the backend cannot send.
- The reasons that travel in a variable are Literal types (edit, move,
  cookies, quota), so the type checker refuses an unknown one too.
- downloads.errors.edit.not_media in EN and HU.

frontend/src/i18n/unusedKeys.contract.test.ts

@@ -3,6 +3,8 @@ import { join } from "node:path";
 import { fileURLToPath } from "node:url";
 import { describe, expect, it } from "vitest";
 
+import { REFUSAL_FAMILIES, type RefusalFamily } from "../lib/api/refusalCodes";
+
 // Every locale key is used by the app. The parity test proves EN and HU agree; nothing proved either
 // one is still READ — 75 keys had outlived the code that showed them (a whole sidebar sort vocabulary,
 // the old login page, a pager the DataTable replaced), each a string a translator would keep in step
@@ -49,9 +51,14 @@ const code = sources(SRC).join("\n");
 const literals = new Set([...code.matchAll(/["'`]([\w.-]+)["'`]/g)].map((m) => m[1]!));
 // Each dynamic key as a SHAPE, every interpolation a `*`: `plex.sort.*`, `editor.*.hint`,
 // `config.choices.*.*` — from a template literal that opens with a key head, or a head concatenated.
+// A refusal's sentence is built from its record (`lib/api/refusalCodes`) rather than a template the
+// scan could read, so each family's prefix is a shape of its own.
 const shapes = [
   ...[...code.matchAll(/`([\w.]+\.(?:\$\{[^}`]*\}|[\w.-])*)`/g)].map((m) => m[1]!),
   ...[...code.matchAll(/["'`]([\w.]+\.)["'`]\s*\+/g)].map((m) => `${m[1]!}\${}`),
+  ...Object.values(REFUSAL_FAMILIES).map(
+    (f: RefusalFamily) => `${f.prefix}.\${reason}${f.suffix ?? ""}`,
+  ),
 ]
   .filter((s) => s.includes("${"))
   .map((s) => s.replace(/\$\{[^}]*\}/g, "*"));