feat(ext/setup): hand off completion to fullscreen vault tab (P2)

After successful device registration (state.configPushed = true), the
wizard now opens vault.html in a new tab and closes the setup tab.
Both create-new and attach-existing flows funnel through the same
finishSetup() handler. Closing the setup tab is best-effort --
chrome.tabs.remove failures don't block the vault open.

Add src/__stubs__/relicario_wasm.stub.ts + vitest.config alias so
setup.ts can be imported in unit tests without the runtime WASM file.
Exclude the stubs dir from the webpack/tsc build in tsconfig.json.

extension/tsconfig.json

@@ -12,5 +12,5 @@
     "baseUrl": "."
   },
   "include": ["src/**/*"],
-  "exclude": ["node_modules", "dist", "wasm", "src/**/__tests__/**"]
+  "exclude": ["node_modules", "dist", "wasm", "src/**/__tests__/**", "src/__stubs__/**"]
 }