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/security/requirements.test.js

@@ -19,20 +19,20 @@ import {
   isValidTarget,
   normalizeAddress,
   reduceAdminState,
-} from "@nostr-governance/core";
+} from "@bitgate/core";
 import {
   MAX_POLICY_BYTES,
   canonicalIdentifier,
   decodePolicy,
   decodeReport,
   verifyEvents,
-} from "@nostr-governance/nostr";
+} from "@bitgate/nostr";
 import {
   ERROR_CODES,
   createCommands,
-  createGovernanceRuntime,
+  createBitGate,
   createMemoryTransport,
-} from "@nostr-governance/runtime";
+} from "@bitgate/runtime";
 
 const ROOT = "a1".repeat(32);
 const MODERATOR = "b2".repeat(32);
@@ -75,7 +75,7 @@ const event = (parts) => ({
 });
 
 function runtimeWithSigner(pubkey) {
-  const runtime = createGovernanceRuntime({
+  const runtime = createBitGate({
     applicationId: "sec",
     namespace: "sec",
     transport: createMemoryTransport(),
@@ -206,7 +206,7 @@ describe("9. ignore unauthorized contributor events", () => {
   });
 
   it("stops honoring an actor's contributions the moment their role is revoked", () => {
-    /** @type {import('@nostr-governance/core').Contribution[]} */
+    /** @type {import('@bitgate/core').Contribution[]} */
     const contributions = [
       { actor: MODERATOR, kind: "user-deny", targets: [{ type: "user", pubkey: CREATOR }] },
     ];
@@ -419,7 +419,7 @@ describe("18-19. transient relay failure and diagnostics", () => {
 
 describe("20. fail closed when authority cannot be confirmed", () => {
   it("refuses an administrative command with no signer", async () => {
-    const runtime = createGovernanceRuntime({
+    const runtime = createBitGate({
       applicationId: "sec",
       namespace: "sec",
       transport: createMemoryTransport(),
@@ -430,7 +430,7 @@ describe("20. fail closed when authority cannot be confirmed", () => {
   });
 
   it("refuses every administrative command when the roster is empty", async () => {
-    const runtime = createGovernanceRuntime({
+    const runtime = createBitGate({
       applicationId: "sec",
       namespace: "sec",
       transport: createMemoryTransport(),