Add unit tests for CommandManager CLI parser

[angeloINTJ]

What

Write host-side unit tests for the CLI command parser in CommandManager.

Why

The CLI is accessible via USB Serial (no auth) and Bluetooth (PIN auth). A parser bug on the unauthenticated USB path could brick the device, corrupt config, or leak data. Currently untested.

How

1. Create test/test_command_parser/test_main.cpp following the pattern of test/test_validators/test_main.cpp
2. Add a test_filter = test_command_parser line or include in native env
3. Test at minimum:
   • Valid commands: help, show system, conf user add ..., clear log confirm
   • Invalid commands: empty string, garbage, buffer overflow at CLI_LINE_MAX=256
   • Edge cases: trailing whitespace, extra spaces between args, Unicode bytes
   • Partial commands: conf without subcommand, show without target
   • Auth boundary: commands available before vs after BT PIN auth

Acceptance

• pio test -e native passes
• Valid commands parse correctly (exact arg extraction)
• Invalid commands return unknown/error without crash
• 256-char boundary is respected
• Tests are self-contained (no hardware)

References

• src/CommandManager.h and src/CommandManager.cpp
• src/SystemDefs_Cli.h — CliDemand struct
• test/test_validators/test_main.cpp — pattern to follow