[sanny32]

Adds optional TLS 1.2+ for Modbus TCP servers. The connection dialog provides a TLS switch and selects port 802 when the default TCP port is used; RTU over TCP keeps its existing behavior.

• Generate a self-signed server certificate automatically on first startup and manage regeneration and public certificate export in Modbus Definitions → Certificates.
• Store the certificate and private key atomically in pki/own/OpenModSim@<hostname>.pem, with owner-only permissions on Unix.
• Accept TLS clients without requiring client certificates. Clients can verify the server certificate; plaintext connections to a TLS listener are rejected. This implements server-authenticated TLS, without mutual client authentication or certificate role enforcement.
• Persist TLS selection in connection settings and projects, add build and packaging support for a single matching OpenSSL version (1.1.1 for Qt 5, 3 for Qt 6), and update translations and documentation.
• Keep certificate settings compact, abbreviate long DNS lists, and give the settings content area a separate background on macOS.

Validation: macOS Qt 6 application build succeeded; all 37 CTest suites passed. Coverage includes certificate generation and persistence, first-run generation, existing/corrupt identities, TLS connections, settings serialization, and translated UI layout in light/dark palettes. Windows and Linux builds were not run locally.

Closes #139.