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/package.json

@@ -0,0 +1,18 @@
+{
+  "name": "nexus-terminal-frontend",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Frontend for Nexus Terminal desktop SSH client",
+  "scripts": {
+    "install:assets": "node scripts/copy-assets.js",
+    "build": "node scripts/build.js",
+    "dev": "node scripts/build.js --watch",
+    "postinstall": "npm run install:assets"
+  },
+  "dependencies": {
+    "xterm": "5.3.0",
+    "xterm-addon-fit": "0.8.0",
+    "xterm-addon-search": "0.13.0",
+    "xterm-addon-web-links": "0.9.0"
+  }
+}