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.

tests/performance/large-feed.test.js

@@ -8,8 +8,8 @@
 
 import { describe, expect, it, vi } from "vitest";
 
-import { createPolicyDefinition } from "@nostr-governance/core";
-import { createGovernanceRuntime, createMemoryTransport } from "@nostr-governance/runtime";
+import { createPolicyDefinition } from "@bitgate/core";
+import { createBitGate, createMemoryTransport } from "@bitgate/runtime";
 
 const AUTHOR_COUNT = 500;
 const TARGET_COUNT = 5_000;
@@ -18,9 +18,9 @@ const NOW = 1_750_000_000;
 
 const hex = (prefix, index) => `${prefix}${index.toString(16).padStart(10, "0")}`.padEnd(64, "0").slice(0, 64);
 
-/** @param {number} index @returns {import('@nostr-governance/core').GovernanceTarget} */
+/** @param {number} index @returns {import('@bitgate/core').GovernanceTarget} */
 const userTarget = (index) => ({ type: "user", pubkey: hex("a", index) });
-/** @param {number} index @param {number} authorIndex @returns {import('@nostr-governance/core').GovernanceTarget} */
+/** @param {number} index @param {number} authorIndex @returns {import('@bitgate/core').GovernanceTarget} */
 const eventTarget = (index, authorIndex) => ({
   type: "event",
   id: hex("c", index),
@@ -55,7 +55,7 @@ const POLICY = createPolicyDefinition({
 /** Build a runtime loaded with a large, realistic governance state. */
 function buildLargeRuntime() {
   const transport = createMemoryTransport();
-  const runtime = createGovernanceRuntime({
+  const runtime = createBitGate({
     applicationId: "perf",
     namespace: "perf",
     transport,