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).

build/windows/info.json

@@ -0,0 +1,15 @@
+{
+	"fixed": {
+		"file_version": "{{.Info.ProductVersion}}"
+	},
+	"info": {
+		"0000": {
+			"ProductVersion": "{{.Info.ProductVersion}}",
+			"CompanyName": "{{.Info.CompanyName}}",
+			"FileDescription": "{{.Info.ProductName}}",
+			"LegalCopyright": "{{.Info.Copyright}}",
+			"ProductName": "{{.Info.ProductName}}",
+			"Comments": "{{.Info.Comments}}"
+		}
+	}
+}