Clarify press key input format

[masnwilliams]

Summary

• document that each --key value accepts one X11 keysym or chord
• add canonical Ctrl+minus and repeated-key examples
• direct users to computer type --text for text input

Rollout

Merge after kernel/kernel-images#364 is deployed so the documented punctuation form is supported by the runtime.

Testing

• make test
• make build
• ./bin/kernel browsers computer press-key --help

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Note

Low Risk
Help text and README only; no runtime or parsing logic changes.

Overview
Documentation-only update for kernel browsers computer press-key: it clarifies how to pass --key values and when to use computer type instead.

The --key flag is described as one X11 keysym or chord per value (examples: Return, Ctrl+t, Ctrl+minus) in both README and press-key --help. A short note explains using multiple --key flags for sequential or repeated presses (e.g. --key BackSpace --key BackSpace) and points users to computer type --text for entering text rather than misusing press-key.

No changes to command behavior or API calls; rollout note in the PR ties the Ctrl+minus example to a separate kernel-images deployment.

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