Add interactive shell mode

[tomkp]

Summary

• Add shell command to CLI that starts an interactive REPL session
• Implement processShellCommand function to handle commands in the shell
• Support for commands: help, select-pse, select-app, read-record, get-data, list-apps, info, quit/exit
• Add comprehensive tests for all shell command handlers

Usage

emv shell

This starts an interactive session where users can issue EMV commands without prefixing each with emv:

emv> help
emv> select-pse
emv> list-apps
emv> select-app a0000000041010
emv> read-record 1 1
emv> quit

Test plan

• All processShellCommand tests pass
• help command shows available commands
• quit/exit commands return exit action
• Commands like select-pse, select-app, etc. delegate to existing functions
• Empty input is ignored
• Unknown commands show helpful error message
• Lint passes
• All 110 tests pass

Closes #65