Fix manual tag on mw_log_backend_architectural_design in score/mw/log/design/backend/BUILD

### What

Fix manual tag on mw_log_backend_architectural_design in score/mw/log/design/backend/BUILD

score_tooling 2.x parses every .puml; the legacy diagrams here are not yet in the parser's supported subset (eclipse-score/tooling#447). The target is kept out of wildcard builds until they are reworked.

This was done to unblock the integration of coverage infra and adjust deps.
The mw_log_backend_architectural_design is not consumed anywhere and was a plumbing activity to support the https://eclipse-score.github.io/tooling/latest/user_guide/general.html#the-dependable-element-concept in the near future.

### Acceptance Criteria (DoD)

All *.puml files are fixed as per the new parser reqs.

### How

_No response_