swarm-ui link-account forms: keep the sent name, drop secrets, one word for forge

The success line of both link forms read the live text field, so editing
the name after a link changed the sentence. The result now carries the
name that was sent.

The matrix form held the typed token and password after a failed submit,
and kept them across a switch of credential mode. It now drops them when
the request ends and when the mode changes.

The linked-accounts list and the delete dialog said forgejo where the
link menu and forms say forge; they now say forge.

frontend/packages/swarm-ui/test/account-kind.test.mjs

@@ -0,0 +1,15 @@
+// The word the linked-accounts list uses for an account kind. Run by `npm
+// test`, which Node runs with its built-in test runner and type stripping,
+// so the `.ts` module is imported as it is.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { accountKindLabel } from "../src/agent/detail/account-kind.ts";
+
+test("a forgejo account is called a forge account, like the link menu does", () => {
+  assert.equal(accountKindLabel("forgejo"), "forge");
+});
+
+test("the other kinds keep their names", () => {
+  assert.equal(accountKindLabel("matrix"), "matrix");
+  assert.equal(accountKindLabel("github"), "github");
+});