feat: complete Tasks 1-3 (setup, models+storage, config management)

- Task 1: Project setup (go.mod, Makefile, .gitignore, main.go)
- Task 2: Core data models (Host, KeyPair, Snippet, AppConfig) + JSON storage layer
- Task 3: Configuration management with cross-platform path support (macOS/Linux/Windows)
- Updated PROJECT_STATE.md with progress tracking

.gitignore

@@ -0,0 +1,42 @@
+# Binaries
+bin/
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary
+*.test
+
+# Output of go coverage
+*.out
+coverage.html
+
+# Dependency directories
+vendor/
+
+# Go workspace
+go.work
+go.work.sum
+
+# IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Environment files
+.env
+.env.local
+
+# Config files (local testing)
+*.local.json
+
+# Build output
+dist/