[codex] fix macOS keyboard layout capture

[louis030195]

Summary

• respect the active macOS keyboard layout when converting captured keycodes into text
• keep the existing US-keyboard fallback for cases where the macOS layout API is unavailable
• add focused coverage for the fallback mapping and Carbon modifier conversion

Why

AZERTY users were seeing captured keyboard input interpreted like QWERTY during meetings because macOS text capture used a hard-coded US key map.

Validation

• cargo check -p screenpipe-a11y
• cargo test -p screenpipe-a11y keycode_mapping
• cargo test -p screenpipe-a11y carbon_modifier_state
• git diff --check