[arenabuddy] Update CLI documentation and fix MTGA database file extension

[gazure]

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

[gazure]

• [arenabuddy] improve scraping of basic land arts #325
• [arenabuddy] add tmnt cards #324
• [arenabuddy] Update CLI documentation and fix MTGA database file extension #323 👈 (View in Graphite)
• [arenabuddy] Fix mulligan decision capitalization from lowercase to title case #322
• [arenabuddy] Convert UI theme from light to dark mode #321
• Remove generated Tailwind CSS file and add to gitignore #320
• Simplify CLAUDE.md development documentation #319
• [arenabuddy] Add automatic match sync from server on login and startup #318
• main

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[gazure]

Merge activity

• Mar 1, 1:19 AM UTC: Graphite rebased this pull request, because this pull request is set to merge when ready.