fix(reset): stop displaying internal entropy

[BitHighlander]

Security invariant

Production firmware must never render or return the 32-byte internal entropy used as seed pre-image material.

Change

• removes the Internal Entropy OLED confirmation path from reset
• removes display_random from the internal reset API
• keeps the legacy protobuf field decodable but ignores it, preserving host wire compatibility
• deletes more code than it adds

Before this change, a host could set ResetDevice.display_random, supply the external entropy, and reconstruct SHA256(internal_entropy || external_entropy) after observing the screen once.

Validation

• clean isolated Docker build
• direct make xunit execution: firmware 388/388, board 2/2, crypto 4/4, Pallas constant-time 7/7
• source audit: no production read of display_random and no Internal Entropy screen remains
• release device build passed (firmware.keepkey.bin: 649,748 bytes)
• bitcoin-only release build passed (firmware.keepkey.bin: 361,076 bytes)

Compatibility

The protobuf schema is unchanged. Hosts that still send display_random=true receive normal reset behavior without an entropy screen.

Hardware check

On an uninitialized test device, send otherwise-identical reset requests with display_random false and true. Both must follow the same PIN/backup flow, and neither may display entropy bytes.

The wider hardening sequence and acceptance gates are tracked in #334.