fix(security): close every finding from the audit

Critical
- Any pubkey could publish a kind:30078 roles document and become root of a
  deployment, granting itself every capability and denying anyone. Roles are now
  accepted only from the configured root, compared against the constructor
  value rather than current authority state so a bad ingest cannot move the
  goalposts. Reproduced end to end before the fix; regression test added.
- Administrative state now fails closed without signature verification. Without
  it, event.pubkey is an unauthenticated claim, so an authorship check alone
  proves nothing — a relay can put the root's key on an event the root never
  wrote. trustUnsignedEvents opts in for local and test use.

High
- Report categories could evade moderation entirely: resolveThresholds used
  bracket truthiness, so "constructor" resolved to the Object constructor (all
  gates undefined) and "__proto__" to Object.prototype, both bypassing the
  default threshold. Own-property lookups and null-prototype tables throughout
  core — policy, evaluator, evidence, authority, presets.
- Live subscriptions bypassed signature verification entirely; an attacker only
  had to wait for the subscription rather than the load.
- The default administrative query asked relays for every kind:30078 and
  kind:30000 event in existence, with no author, identifier, or limit. Now
  filtered to governance identifiers with a bounded limit.

Medium
- Cached state was trusted as authority: a cache naming a different root is now
  rejected, so same-origin tampering cannot persist a takeover.
- Provider attribute changes silently stopped working after the first one, and
  concurrent starts leaked a transport. Generation-guarded.
- Unbounded growth in the report store, mute store, decision cache, and the
  transport's per-subscription dedupe set — all now capped.

Also restores the on-wire `d` identifier to <namespace>:governance:<scope>:v1.
The BitGate rename replaced "governance:" too broadly and silently changed the
event format; both encoder and parser changed together, so round-trip tests
never noticed. The identifier names the kind of document, not the library.

Adds docs/security.md and 21 regression tests reproducing each finding.

832 tests.

packages/runtime/test/runtime.test.js

@@ -72,6 +72,8 @@ function makeRuntime(events = []) {
     transport,
     policy: POLICY,
     now: () => NOW,
+    root: ROOT,
+    trustUnsignedEvents: true,
   });
   return { runtime, transport };
 }
@@ -132,7 +134,9 @@ describe("construction", () => {
   it("changes its storage key when the root authority changes", () => {
     const { runtime } = makeRuntime();
     const before = runtime.storageKeyFor("admin");
-    runtime.admin.setRoles({ root: ROOT, actors: {} });
+    // Rotating the root must invalidate the cache namespace so a new
+    // administration cannot inherit the previous one's stored state.
+    runtime.admin.setRoles({ root: CREATOR, actors: {} });
     expect(runtime.storageKeyFor("admin")).not.toBe(before);
   });
 });
@@ -266,6 +270,8 @@ describe("loadAdministrativeState", () => {
       transport,
       policy: POLICY,
       now: () => NOW,
+      root: ROOT,
+      trustUnsignedEvents: true,
     });
 
     await runtime.loadAdministrativeState({ authors: [MODERATOR] });
@@ -284,6 +290,8 @@ describe("active targets and subscriptions", () => {
       policy: POLICY,
       now: () => NOW,
       chunkSize: 2,
+      root: ROOT,
+      trustUnsignedEvents: true,
     });
 
     runtime.setActiveTargets([
@@ -305,6 +313,8 @@ describe("active targets and subscriptions", () => {
       transport,
       policy: POLICY,
       now: () => NOW,
+      root: ROOT,
+      trustUnsignedEvents: true,
     });
 
     runtime.setActiveTargets([