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/testing/src/conformance.js

@@ -1,4 +1,4 @@
-// Conformance harness for @nostr-governance
+// Conformance harness for BitGate
 //
 // Turns a JSON fixture into a snapshot, evaluates it, and compares the decision
 // against the fixture's expectation. Expectations are partial by design: a
@@ -11,7 +11,7 @@ import {
   createViewerState,
   evaluateTarget,
   reduceAdminState,
-} from "@nostr-governance/core";
+} from "@bitgate/core";
 
 /**
  * @typedef {Object} FixtureExpectation
@@ -78,8 +78,8 @@ export function buildSnapshot(fixture) {
 /**
  * Evaluate a fixture against a policy definition.
  * @param {Object} fixture
- * @param {import('@nostr-governance/core').PolicyDefinition} policy
- * @returns {import('@nostr-governance/core').GovernanceDecision}
+ * @param {import('@bitgate/core').PolicyDefinition} policy
+ * @returns {import('@bitgate/core').GovernanceDecision}
  */
 export function evaluateFixture(fixture, policy) {
   const { snapshot, viewer } = buildSnapshot(fixture);
@@ -93,7 +93,7 @@ export function evaluateFixture(fixture, policy) {
 
 /**
  * Compare a decision against a fixture expectation.
- * @param {import('@nostr-governance/core').GovernanceDecision} decision
+ * @param {import('@bitgate/core').GovernanceDecision} decision
  * @param {FixtureExpectation} expectation
  * @returns {string[]} Human-readable mismatches; empty when the fixture passes
  */
@@ -187,8 +187,8 @@ export function diffExpectation(decision, expectation) {
 /**
  * Run one fixture end to end.
  * @param {Object} fixture
- * @param {import('@nostr-governance/core').PolicyDefinition} policy
- * @returns {{ passed: boolean, mismatches: string[], decision: import('@nostr-governance/core').GovernanceDecision }}
+ * @param {import('@bitgate/core').PolicyDefinition} policy
+ * @returns {{ passed: boolean, mismatches: string[], decision: import('@bitgate/core').GovernanceDecision }}
  */
 export function runConformanceCase(fixture, policy) {
   const decision = evaluateFixture(fixture, policy);