feat: rename to BitGate and close the drop-in gap

Renames the project and makes it as easy to adopt as BitLogin, which was the
stated bar and which it did not previously meet.

Rename (ADR 0005): @nostr-governance/* -> @bitgate/*, governance-* elements ->
bitgate-*, createGovernanceRuntime -> createBitGate. "Governance" reads as DAO
voting to this audience and named a category rather than a product; BitGate
names the benefit and joins the bit- family that BitVid and BitRoad compose
with. Domain types keep their names — the product is BitGate, the subject
matter is still governance. The migration plan is left as written; this ADR
records the change rather than rewriting history.

Drop-in distribution (ADR 0006): adopting BitGate meant supplying a transport,
authoring a policy, and wiring every element in JavaScript. Now:

- createRelayTransport(urls) — WebSocket transport with reconnection, backoff,
  subscription replay, and cross-relay dedupe
- policy presets (social, commerce, admin-only) addressable by name; the engine
  still carries no thresholds of its own
- <bitgate-provider> — configuration in markup, with descendants finding the
  runtime through a bubbling context event rather than DOM walking, which
  breaks across shadow boundaries
- npm run build:widget — a self-contained dist/bitgate.js

That last one came from running it in a browser rather than from a test. Bare
specifiers resolve in Node and vitest but not in a browser, so the widget
source worked everywhere except a plain static page — the one place it exists
to serve. The bundle is not committed: consumers build from reviewed source.

Also found by running it: the provider's ready event fires during element
upgrade, before a page that defines elements after parsing can attach a
listener, so it now exposes `ready` as a promise too.

Four bugs fixed along the way, three found by new tests and one by the browser:
admin state stayed silent when a roster change altered capabilities but no
denials; the relay transport sent every subscription twice on connect; the
commerce preset computed a meaningless visibility verdict at checkout and could
hide a listing from its own seller; <bitgate-status> threw on an unusable
decision.

759 tests; lint, typecheck, and both builds clean.

packages/runtime/test/commands.test.js

@@ -1,10 +1,10 @@
 import { describe, expect, it, vi } from "vitest";
 
-import { createPolicyDefinition } from "@nostr-governance/core";
-import { REPORT_KIND, encodeRoles } from "@nostr-governance/nostr";
+import { createPolicyDefinition } from "@bitgate/core";
+import { REPORT_KIND, encodeRoles } from "@bitgate/nostr";
 
 import { ERROR_CODES, createCommands } from "../src/commands.js";
-import { createGovernanceRuntime } from "../src/runtime.js";
+import { createBitGate } from "../src/runtime.js";
 import { createMemoryTransport } from "../src/interfaces.js";
 
 const ROOT = "a1".repeat(32);
@@ -45,7 +45,7 @@ function signerFor(pubkey) {
  */
 function setup({ actor = MODERATOR, signer, transport } = {}) {
   const memory = transport ?? createMemoryTransport();
-  const runtime = createGovernanceRuntime({
+  const runtime = createBitGate({
     applicationId: "test",
     namespace: "app",
     transport: memory,
@@ -177,7 +177,7 @@ describe("argument validation", () => {
 
 describe("signer failures", () => {
   it("reports a missing signer", async () => {
-    const runtime = createGovernanceRuntime({
+    const runtime = createBitGate({
       applicationId: "test",
       namespace: "app",
       transport: createMemoryTransport(),
@@ -244,7 +244,7 @@ describe("contribution round-trip", () => {
     const { runtime, commands, transport } = setup();
     await commands.denyUser(CREATOR);
 
-    const fresh = createGovernanceRuntime({
+    const fresh = createBitGate({
       applicationId: "test",
       namespace: "app",
       transport: createMemoryTransport(),