This pull request updates the CLI documentation and fixes a critical bug in the MTGA database detection logic.

Documentation Updates:

• Clarified that the CLI tool is named arenabuddyctl
• Added comprehensive examples showing how to run commands using cargo run -p arenabuddy_cli
• Documented the new scrape-mtga command with auto-detection of MTGA install paths and custom path options
• Added examples for the REPL and event-log commands
• Updated help command examples to use the correct cargo syntax

Bug Fix:

• Fixed incorrect file extension filter in MTGA database detection - changed from .rs to .mtga to properly locate Raw_CardDatabase_*.mtga files