feat: scaffold matrix_client_pc (Wails + React-TS + mautrix-go + keyring)

Initial scaffold for issue 0147. App lives at
projects/element_agents/apps/matrix_client_pc/.

Deps:
- github.com/wailsapp/wails/v2 v2.11.0
- maunium.net/go/mautrix v0.25.2
- github.com/zalando/go-keyring v0.2.6

Next: MatrixService bindings + Login/Home React screens + helpers
(matrix_client_init, mas_oidc_loopback, keyring_token_store).

wails.json

@@ -0,0 +1,13 @@
+{
+  "$schema": "https://wails.io/schemas/config.v2.json",
+  "name": "matrix_client_pc",
+  "outputfilename": "matrix_client_pc",
+  "frontend:install": "npm install",
+  "frontend:build": "npm run build",
+  "frontend:dev:watcher": "npm run dev",
+  "frontend:dev:serverUrl": "auto",
+  "author": {
+    "name": "Egutierrez",
+    "email": "egutierrez@dead.dd"
+  }
+}