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

wails.json

@@ -0,0 +1,19 @@
+{
+  "$schema": "https://wails.io/schemas/config.v2.json",
+  "name": "nexus-terminal",
+  "outputfilename": "NexusTerminal",
+  "frontend:install": "npm install",
+  "frontend:build": "npm run build",
+  "frontend:dev:watcher": "npm run dev",
+  "frontend:dev:serverUrl": "auto",
+  "author": {
+    "name": "Nexus Terminal Contributors"
+  },
+  "info": {
+    "companyName": "Nexus Terminal",
+    "productName": "Nexus Terminal",
+    "productVersion": "0.1.0",
+    "copyright": "Copyright © 2024 Nexus Terminal Contributors",
+    "comments": "A premium desktop SSH, Telnet, and RAW TCP client"
+  }
+}