fix: clarify inherited key display

[IgorArkhipov]

Problem

https://t.me/c/1464748383/37027/132146

Inherit (KC_TRNS) was rendered as the keycode from a lower-numbered layer in several UI and layout-export views. This suggested that the displayed key would always run, even though firmware resolution instead follows the active layer stack.

Fix

• Render every Inherit assignment as a dimmed ▽ marker instead of resolving and displaying a lower-layer keycode.
• Apply the marker consistently to keyboard keys, encoder rotation and press assignments, Sticky Layout preview, and PNG/SVG/PDF layout exports.
• Keep None behavior unchanged; this PR only corrects the representation of Inherit.

Verification

• cargo test --bin entropy -- --quiet: 321 passed.
• Scoped rustfmt --check and git diff --check: passed.