frank-medium: pass --mmproj explicitly; this build has no autoload

The 36:29/327680/vision deploy came up healthy and text-only: image requests
answered 500 'image input is not supported - hint: ... provide the mmproj'
with no mmproj line in the load log, so llama-server fb27a525 does not
autoload mmproj*.gguf from the model directory. Name the file, the way
frank-small's serve script already does, and pin the flag in the seam.

tests/frank_medium_unit.bats

@@ -230,7 +230,8 @@ print('draft-model wiring ok')
     grep -q '^NO_MMPROJ=0$' "$ENV_FILE"
     grep -q '^MM_PROJ_FILE=mmproj-BF16.gguf$' "$ENV_FILE"
     # The serve script refuses to start without the projector when vision is
-    # on, so a missing file is a deploy error, not a silent text-only server.
+    # Explicit flag, not autoload: this build starts text-only without it.
+    grep -q -- '--mmproj "$MM_PROJ"' "$SERVE"
     grep -q 'vision is enabled but the projector is missing' "$SERVE"
     # And the download script fetches and byte-verifies it.
     grep -q '^MM_PROJ_SIZE=931145888$' "$FETCH"