kv-wasm: onboarding (setup codes, enrollment tickets, scan-to-join) for the web vault

Mirrors kv-ffi's docs/10 §5 API in WebCore and binds it under the names the web app codes
against: setupPayloadForKit, addDevicePayload, revokeEnrollmentTicket, loginWithSetup,
joinStart/joinPoll/joinCancel, joinApprove, joinSend, and the free function parseSetupPayload
(also callable through the worker client).

Unlike kv-ffi, the Secret Key is not persisted: every unlock on the web takes it, so it is
kept zeroized in the unlocked state and dropped on lock. loginWithSetup refuses a code for a
different server than the configured origin (the browser only talks to its own origin).

Tests: ticket enrollment and scan-to-join in both roles against kv-ffi via the kv-sync test
server, a swapped-approver rejection, a Chrome test (IndexedDB never holds the Secret Key,
JS shapes, error codes) and a Node smoke check of the built package.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

crates/kv-wasm/js/worker.js

@@ -56,7 +56,7 @@ async function open(dbName, inMemory) {
   return null;
 }
 
-const FREE_FUNCTIONS = new Set(["generatePassword", "totpCode", "matchUrl", "coreVersion"]);
+const FREE_FUNCTIONS = new Set(["generatePassword", "totpCode", "matchUrl", "coreVersion", "parseSetupPayload"]);
 
 self.onmessage = async ({ data: { id, method, args } }) => {
   try {