security: announce a fresh EIP-6963 provider UUID per page load (closes #398)

The provider UUID was generated once, kept in extension storage and
announced to every page on every load, so any site could read it as a
stable identifier for the install across sites and browser restarts.

inpage.js now generates one UUID per page load, shared by every
announcement in that load, and stores nothing. The eip6963Uuid storage
key and the AUTISTMASK_PROVIDER_UUID content-script message are removed.
The key was never part of the versioned autistmask profile, so the state
schema is untouched. Two inpage.js message listeners lose the leftover
name onUuid.

The test posts each load the same stored UUID the way the old content
script did, and asserts that no load announces it and that two loads
announce different UUIDs.

Model: opus-5-5

src/content/inpage.js

@@ -45,7 +45,7 @@
     }
 
     // Listen for responses from the content script
-    window.addEventListener("message", function onUuid(event) {
+    window.addEventListener("message", (event) => {
         if (event.source !== window) return;
         if (event.data?.type !== "AUTISTMASK_RESPONSE") return;
         const { id, result, error } = event.data;
@@ -60,7 +60,7 @@
     });
 
     // Listen for events pushed from the extension
-    window.addEventListener("message", function onUuid(event) {
+    window.addEventListener("message", (event) => {
         if (event.source !== window) return;
         if (event.data?.type !== "AUTISTMASK_EVENT") return;
         const { eventName, data } = event.data;

tests/inpageProviderUuid.test.js

@@ -96,7 +96,7 @@ const UUID_V4 =
     /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
 
 describe("the EIP-6963 provider UUID is fresh per page load", () => {
-    test("a load announces a UUIDv4 without being asked", () => {
+    test("a load announces a UUIDv4", () => {
         const uuids = announcedUuids();
         expect(uuids.length).toBeGreaterThan(0);
         expect(uuids[0]).toMatch(UUID_V4);