Initial commit: Nextcloud integration with Files, Contacts, Calendar, and Mail

- CLI tools: nextcloud-client, nextcloud-contacts, nextcloud-calendar, nextcloud-mail
- Build script with compile-time credentials
- Skills for all four tools
- Full documentation and examples
- Email tool supports IMAP/SMTP with attachment download
- SSL/TLS support with optional certificate validation

.gitignore

@@ -0,0 +1,31 @@
+# Credentials and sensitive data
+CREDENTIALS.md
+
+# Compiled binaries
+tools/go/*/nextcloud-*
+
+# Go build artifacts
+tools/go/*/*.exe
+tools/go/*/*.exe~
+tools/go/*/*.dll
+tools/go/*/*.so
+tools/go/*/*.dylib
+tools/go/*/bin/
+tools/go/*/dist/
+
+# Test binaries
+tools/go/*/*-test
+
+# Go module cache
+tools/go/*/go.sum
+
+# IDE files
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS files
+.DS_Store
+Thumbs.db