Add display mode and completion option snippets (cmdline, graphical, text, vnc, halt, poweroff, reboot, shutdown)

[sfloess]

Part of #15: Include all option snippets as found in the kickstart guide.

Scope

Add option snippets for display mode and installation completion kickstart commands. The existing completion_method snippet may partially cover completion, but individual command snippets are needed:

Display/UI mode:

• cmdline - Perform installation in command-line mode (no interaction)
• graphical - Perform installation in graphical mode (default)
• text - Perform installation in text mode
• vnc - Allow remote viewing of graphical installation via VNC (vnc [--host= --port= --password=])

Completion method:

• halt - Halt the system after installation completes
• poweroff - Power off the system after installation completes
• reboot - Reboot after installation completes (reboot [--eject] [--kexec])
• shutdown - Shut down the system after installation completes

Notes

Review the existing completion_method snippet to determine if it already covers halt/poweroff/reboot/shutdown, or if individual snippets should supplement it.

Reference

RHEL 7 Kickstart Syntax Reference - Section 27.3

Acceptance Criteria

• Each command has a corresponding snippet file under snippets/options/
• Snippets follow the existing pattern/style used by other option snippets in the repo
• No duplication with existing completion_method snippet (refactor if needed)