Support reading stdin in CLI to make `echo ... | commit-check --flag` work

### What's the problem this feature will solve?

read stdin in the CLI so `echo ... | commit-check --flag` works.

### Describe the solution you'd like

Implementing stdin support by adding optional text overrides to check functions and wiring stdin reading in the CLI so `echo ... | commit-check --flag` works.


### Additional context

_No response_