[JaxCalder]

Serial terminal output on STM32F746G-DISCO contains bare LF bytes, so minicom advances the row without returning to column zero. Add default LF-to-CRLF output processing in dmtty's line discipline, shared by application writes and input echo, before forwarding to the backing stream or kernel fallback.

Output processing is independent of echo/canonical input flags: dmell temporarily clears both while editing commands, and Enter still needs CRLF. Existing CRLF is preserved across calls and handles. Per-node serialization and short-write accounting prevent duplicate CR on retries. The new onlcr configuration key and appended get/set ioctls allow byte-exact output when needed; previous ioctl numbers are unchanged. UART drivers and ordinary file writes retain their existing behavior.

Validation:

• Created the branch from freshly fetched origin/main (e8d09f5).
• Native module build and Cortex-M7 module build pass.
• Host regression harness passes using both native and ARM build headers; added it to CI. Covers LF/CRLF, split handles, partial writes (including failure after inserted CR), input flags independent of output, all 256 byte values with output processing disabled, output ioctls, kernel fallback, and canonical echo.
• Built dmod-boot for BOARD=stm32f746g-disco with the local module and flashed via ST-Link (Verified OK). Raw UART capture at 921600 baud: before the fix, echo produced three bare LFs; after the fix, echo, multiline help, and ls /dev contain only CRLF, including the shell's Enter echo, with no CRCRLF.
• On the board, YMODEM received two files totaling 5130 bytes, including every byte value, with zero retransmissions. Read back a 1034-byte NUL-free binary file and matched the exact expected terminal CRLF conversion. Console output remains correct after the transfer.

Compatibility: clients sending arbitrary binary output through a TTY must explicitly disable onlcr (or use the backing device directly). Disabling canonical input alone intentionally keeps terminal output processing enabled. The YMODEM receiver's binary input and LF-free output protocol bytes are unaffected.