refactor: reorganize project into monorepo with frontend scaffolding

Convert project from single backend to monorepo structure with separate
frontend (Vue 3 + TypeScript + Vite) and backend directories. Updates
all configuration files and build system to support both workspaces.

Ref: T007 (specs/001-modbus-relay-control)

.gitignore

@@ -21,16 +21,32 @@ target/
 coverage/
 
 # Frontend
-## Nuxt dev/build outputs
+## Build outputs
 .output
 .data
 .nuxt
 .nitro
 .cache
 dist
+dist-ssr
+*.local
 
-## Node dependencies
+## Node dependencies and logs
 node_modules
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+## Editor directories (keep .vscode/extensions.json)
+.vscode/*
+!.vscode/extensions.json
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?
 
 # Nix
 result