Add direct SDO CAN map clear action

[Modellfan]

Summary

Add a dedicated "Remove all mappings" action for libopeninverter CAN mapping that uses a direct SDO write instead of the terminal command transport. Button was anyways dead and copy and paste error from uart backend.

Changes

• replace the CAN mapping clear button handler with a confirmation flow in the web UI
• add a frontend CAN-map clear request path that reloads the table after success
• add /canmap?clear=1 support in the firmware CAN map handler
• send SDO write 0x5002 / subindex 4 / data 0 and require the matching SDO write reply before reporting success

[jsphuebner]

Looks good, thanks!
if you want: #20

[Modellfan]

jsphuebner/stm32-sine#58

Also includes the updated libinv to make this function available in stm sine main you also need to merge it

[Modellfan]

This commit crashes the CAN bus update. I froze my sdu with it yesterday. Likely the ongoing CAN Map polling is interrupting the upload. Fix to come. Maybe stage the merge for now.