Extract CLI option parsing and add regression tests

[raphael-solace]

Why: Locks down shortcut modes, defaults, and argument behavior so the rest of the QoL work can be added safely.

Stack note: Stack root; review against main.

Implementation notes:

• Default PrettyDump behavior remains unchanged unless the new flags are used.
• This branch is part of the 10-PR QoL series and should be reviewed in order.

Verification:

• JAVA_HOME="$HOME/AnypointCodeBuilder/java/jdk-17.0.13+11/Contents/Home" ./gradlew clean test installDist --no-daemon
• build/staged/bin/prettydump --help