Add Go project scaffold for Wails v2 SSH/Telnet/RAW TCP client

- go.mod with Wails v2.9.2, x/crypto, go-sqlite3, go-keyring, uuid
- cmd/app/main.go: Wails entry point (Nexus Terminal, 1400x900, #1a1a2e)
- internal/app/app.go: lifecycle (Startup/Shutdown/DomReady)
- internal/models/models.go: full model definitions (Profile, SSHConfig,
  TelnetConfig, RAWConfig, SessionInfo, KnownHost, AppPreferences, etc.)
- internal/models/defaults.go: default values and NewProfile factory
- internal/validation/validation.go: thorough field-level validation
- frontend/embed.go: embedded frontend assets
- Updated existing storage, secrets, config to match new model structure

frontend/embed.go

@@ -0,0 +1,9 @@
+// Package frontend provides the embedded frontend assets for the Wails application.
+package frontend
+
+import "embed"
+
+// Assets contains the built frontend files from the dist directory.
+//
+//go:embed all:dist
+var Assets embed.FS