feat(docker): support a multimodal projector via --mmproj

Vision-capable GGUFs need a separate projector (mmproj) that maps image
embeddings into the text model's space. Add `mmproj` and `mmproj_offload`
as config keys and CLI overrides, and pass them through to llama-server.

The projector path resolves under hf_home exactly like model_path, so it
is covered by the existing read-only mount. validate_model_path() now also
checks the projector, which means --change rejects a missing one *before*
it removes the running container.

--no-mmproj-offload is suppressed when no projector is configured, since
llama.cpp rejects the flag on its own.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_actions.py

@@ -213,3 +213,34 @@ def test_container_lock_force_bypasses_busy(tmp_path, capsys):
             entered = True
     assert entered is True
     assert "busy lock" in capsys.readouterr().err
+
+
+# --- model / mmproj path validation ---------------------------------------
+
+
+def test_validate_model_path_accepts_existing_model(tmp_path):
+    (tmp_path / "m.gguf").write_bytes(b"x")
+    cfg = make_cfg(hf_home=tmp_path, model_path="m.gguf")
+    actions.validate_model_path(cfg)  # must not raise
+
+
+def test_validate_model_path_rejects_missing_model(tmp_path):
+    cfg = make_cfg(hf_home=tmp_path, model_path="absent.gguf")
+    with pytest.raises(FileNotFoundError, match="model file not found"):
+        actions.validate_model_path(cfg)
+
+
+def test_validate_model_path_rejects_missing_mmproj(tmp_path):
+    # The model exists but the configured projector does not: --change must fail
+    # here, before the running container is removed.
+    (tmp_path / "m.gguf").write_bytes(b"x")
+    cfg = make_cfg(hf_home=tmp_path, model_path="m.gguf", mmproj="absent-proj.gguf")
+    with pytest.raises(FileNotFoundError, match="mmproj file not found"):
+        actions.validate_model_path(cfg)
+
+
+def test_validate_model_path_accepts_existing_mmproj(tmp_path):
+    (tmp_path / "m.gguf").write_bytes(b"x")
+    (tmp_path / "proj.gguf").write_bytes(b"x")
+    cfg = make_cfg(hf_home=tmp_path, model_path="m.gguf", mmproj="proj.gguf")
+    actions.validate_model_path(cfg)  # must not raise