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).

app.md

@@ -0,0 +1,50 @@
+---
+name: matrix_client_pc
+lang: go
+domain: infra
+version: 0.1.0
+description: "Cliente Matrix nativo para PC (Win/Linux/macOS) construido con Wails (Go) + React+Mantine+@fn_library. Login MAS OIDC, chat E2EE, calls LiveKit, widgets embebidos. Reemplaza Element Web para uso interno del registry."
+tags: [matrix, element, wails, react, mantine, livekit, e2ee, widgets, agents, mas-migration, client]
+uses_functions:
+  - matrix_client_init_go_infra
+  - mas_oidc_loopback_go_infra
+  - keyring_token_store_go_infra
+uses_types: []
+framework: "wails"
+entry_point: "main.go"
+dir_path: "projects/element_agents/apps/matrix_client_pc"
+repo_url: "https://gitea-dgg044oo04woo4ggcsws4gk0.organic-machine.com/dataforge/matrix_client_pc.git"
+icon:
+  phosphor: "chat-circle"
+  accent: "#7c3aed"
+---
+
+## Goal
+
+Cliente Matrix nativo PC. Login MAS OIDC, chat + E2EE, calls LiveKit, widgets embebidos (Matrix Widget API v2). Reusa funciones del registry para todo lo reutilizable. Frontend Mantine + @fn_library, backend Go con mautrix-go.
+
+## Ejecutar
+
+```bash
+cd projects/element_agents/apps/matrix_client_pc
+wails dev                 # hot-reload + Chrome devtools
+wails build               # binario de release
+```
+
+## Arquitectura
+
+```
+main.go            entry: wails.Run + bind MatrixService
+app.go             struct base App
+matrix_service.go  bindings hacia frontend (Login/GetSession/Logout/...)
+frontend/          React+Vite+TS+Mantine+@fn_library
+  src/
+    App.tsx        router (Login | Home)
+    Login.tsx      boton "Sign in with Matrix" -> abre browser
+    Home.tsx       muestra perfil + boton Logout
+    fn_library/    symlink a frontend/functions/ui del registry
+```
+
+## Capability growth log
+
+- v0.1.0 (2026-05-24) — baseline scaffold (issue 0147): Wails skeleton, login MAS OIDC, token persistence keyring SO.