Add BitLogin as the primary sign-in method (gated, unstable)

The login modal now shows <bitlogin-auth> -- a portable Nostr identity
behind a login name and password -- as the default sign-in path,
styled with bitvid's own brand tokens (accent-strong, surfaces, radii).
The existing NIP-07 extension, nsec, and NIP-46 remote-signer options
still work exactly as before, just collapsed under a new "Other login
options" fold instead of a flat "Available methods" grid; nip07 no
longer carries the stale "Recommended" eyebrow now that BitLogin has
that role.

BitLogin isn't a single button-click-then-await-a-promise flow like
the other providers -- it's a whole multi-screen sign-in/create/recover
UI -- so it gets a permanent, statically-declared widget in
components/login-modal.html (js/ui/bitloginModalIntegration.js relocates
it, never destroys and recreates it, since removal tears down its crypto
Web Worker) instead of a grid button. It still goes through the exact
same session-establishment path as every other signer: a new "bitlogin"
provider (js/services/authProviders/bitlogin.js) lets AuthService
resolve and activate it via the normal requestLogin -> handleAuthLogin
path, while providersForModal excludes it from the grid so it isn't
rendered twice.

Two things this needed beyond the wiring itself:
- js/app.js is one line from its lint/file-size ceiling, so the only
  change there is renaming an import binding (providers -> providersForModal),
  a net-zero line change. The actual widget/event wiring lives in a new,
  unconstrained module instead.
- The login modal's HTML (including the permanent widget element) loads
  asynchronously after bootstrap runs, so wireBitloginLogin() waits via
  MutationObserver rather than assuming a specific call order.

Vendored via scripts/build-bitlogin-widget.mjs (mirrors the existing
Bitcoin Connect/Blossom vendor steps): BitLogin isn't published to npm,
so the widget build is copied verbatim from the sibling ../bitlogin
checkout into committed vendor/bitlogin/, then lazy-imported (like
Bitcoin Connect) so its ~350KB never weighs on visitors who never open
the login modal.

Gated behind FEATURE_BITLOGIN (config/instance-config.js), default on
for this unstable-branch experiment per AGENTS.md §1 -- reset to false
before this reaches main until verified end-to-end against production
relays.

Verified: npm run lint (clean), the full auth/login test suite (43/43,
including new coverage for the provider + adapter), and a manual
Chrome pass against the built dist/ -- widget renders themed correctly,
"Other login options" still shows the original four methods unchanged.

js/services/authProviders/bitlogin.js

@@ -0,0 +1,85 @@
+import { accessControl } from "../../accessControl.js";
+
+const PROVIDER_ID = "bitlogin";
+const PROVIDER_LABEL = "BitLogin";
+const PROVIDER_DESCRIPTION =
+  "A portable Nostr identity behind a familiar login name and password.";
+const PROVIDER_CAPABILITIES = Object.freeze([
+  Object.freeze({
+    id: "signing",
+    label: "Signs Nostr events",
+    variant: "info",
+  }),
+  Object.freeze({
+    id: "portable",
+    label: "Works on every BitLogin site",
+    variant: "neutral",
+  }),
+]);
+const PROVIDER_BUTTON = Object.freeze({
+  variant: "primary",
+});
+const PROVIDER_MESSAGES = Object.freeze({
+  loading: "Signing in with BitLogin…",
+  slow: "Still waiting on BitLogin…",
+  error: "Failed to sign in with BitLogin. Please try again.",
+});
+
+// Set by the widget's own "bitlogin-login" listener (js/ui/applicationBootstrap.js)
+// right before it calls authService.requestLogin({ providerId: "bitlogin" }): by
+// the time that reaches this provider's login(), the widget has already run its
+// own multi-screen sign-in/create/recover flow and produced a pubkey + signer.
+// This provider exists so that result goes through the exact same session-
+// establishment path (AuthService.login -> handleAuthLogin) as every other
+// signer, without BitLogin also rendering as a redundant button in the login
+// grid -- see providersForModal in ./index.js.
+let pendingResult = null;
+
+export function setPendingBitloginResult(result) {
+  pendingResult = result && typeof result === "object" ? result : null;
+}
+
+export default {
+  id: PROVIDER_ID,
+  label: PROVIDER_LABEL,
+  description: PROVIDER_DESCRIPTION,
+  eyebrow: "Recommended",
+  tone: "accent",
+  badgeVariant: "info",
+  capabilities: PROVIDER_CAPABILITIES,
+  button: PROVIDER_BUTTON,
+  messages: PROVIDER_MESSAGES,
+  errorMessage: PROVIDER_MESSAGES.error,
+  async login({ nostrClient } = {}) {
+    const result = pendingResult;
+    pendingResult = null;
+
+    if (!result || typeof result.pubkey !== "string" || !result.pubkey.trim()) {
+      const error = new Error("BitLogin sign-in hasn't completed yet.");
+      error.code = "provider-unavailable";
+      throw error;
+    }
+
+    const pubkey = result.pubkey.trim();
+
+    if (!accessControl.canAccess(pubkey)) {
+      if (accessControl.isBlacklisted(pubkey)) {
+        throw new Error("Your account has been blocked on this platform.");
+      }
+      throw new Error("Access restricted to admins and moderators users only.");
+    }
+
+    if (
+      nostrClient?.signerManager &&
+      typeof nostrClient.signerManager.setActiveSigner === "function"
+    ) {
+      nostrClient.signerManager.setActiveSigner(result.signer);
+    }
+
+    return {
+      authType: PROVIDER_ID,
+      pubkey,
+      signer: result.signer,
+    };
+  },
+};

js/services/authProviders/index.js

@@ -2,6 +2,7 @@ import nip07 from "./nip07.js";
 import nip46 from "./nip46.js";
 import nsec from "./nsec.js";
 import generate from "./generate.js";
+import bitlogin from "./bitlogin.js";
 
 function normalizeProviderId(provider, fallbackId) {
   if (provider && typeof provider.id === "string") {
@@ -39,7 +40,7 @@ function normalizeProviderMetadata(provider, fallbackId) {
   return Object.freeze({ id, label, description, badgeVariant });
 }
 
-const providerList = [nip07, nip46, nsec, generate].filter(Boolean);
+const providerList = [nip07, nip46, nsec, generate, bitlogin].filter(Boolean);
 const providerMap = {};
 const metadataMap = {};
 
@@ -97,6 +98,19 @@ builtInMetadata.forEach((entry) => {
 export const providers = Object.freeze({ ...providerMap });
 export const providerMetadata = Object.freeze({ ...metadataMap });
 
+// BitLogin gets its own permanent, always-visible widget in the login modal
+// (components/login-modal.html) rather than a grid button -- it isn't a single
+// button-click-then-await-a-promise flow like the others, it's a whole
+// multi-screen sign-in/create/recover UI. Excluding it here keeps the modal's
+// provider grid ("Other login options") free of a redundant, do-nothing button
+// for it, while `providers.bitlogin` above still resolves normally for
+// AuthService.requestLogin({ providerId: "bitlogin" }).
+export const providersForModal = Object.freeze(
+  Object.fromEntries(
+    Object.entries(providerMap).filter(([id]) => id !== "bitlogin"),
+  ),
+);
+
 const unknownMetadataCache = new Map();
 
 function getFallbackMetadata(providerId) {

js/services/authProviders/nip07.js

@@ -49,7 +49,6 @@ export default {
   id: PROVIDER_ID,
   label: PROVIDER_LABEL,
   description: PROVIDER_DESCRIPTION,
-  eyebrow: "Recommended",
   tone: "accent",
   badgeVariant: "info",
   capabilities: PROVIDER_CAPABILITIES,