fix: resolve all 8 deployment pipeline breaks

Breaks found and fixed:

1. Dockerfile: COPY 5 individual files → COPY entire ex_engine/
2. patch_ops.sh EX_ENGINE_DIR: /workspace/ex_engine not found → added fallback
3. patch_ops.sh deploy: ix_ops.py to ex_engine/ (flat) → ex_engine/python/ (correct package)
4. ix_startup_patch.py: import from vllm.ex_engine.patch_vllm_ops → vllm.ex_engine.python.patch_vllm_ops
5. ix_moe_bridge.so: only deployed to ex_engine/ → also copy to model_executor/models/ and vllm root
6. ex_engine/__init__.py: missing re-exports → add imports so 'from vllm.ex_engine import x' works
7. gemm_grouped.so: compiled but never imported → add import + flag + prefill GEMM path in qwen3_5.py
8. build_moe_bridge.sh Python heredoc: SCRIPT_DIR not exported + wrong nested path → export + search both layouts

Also added:
- CUTLASS batched GEMM compile step (corex_batched_gemm.so for decode)
- Full ex_engine/python/*.py deployment (was deploying only 2 of 19 files)
- EX_ENGINE_INFRA_AUDIT.md documenting all findings

build_moe_bridge.sh

@@ -75,14 +75,28 @@ echo "[moe_bridge] ixformer .so count: ${#IX_SO_FILES[@]}"
 # --- Build via torch.utils.cpp_extension ---
 mkdir -p "${SCRIPT_DIR}/prebuilt"
 
+export SCRIPT_DIR VLLM_ROOT
 python3 << 'PYEOF'
 import os, sys, glob, shutil
 
 script_dir = os.environ.get("SCRIPT_DIR", ".")
 vllm_root = os.environ.get("VLLM_ROOT", "")
 
-moe_cu = os.path.join(script_dir, "ex_engine", "csrc", "moe_ops_impl.cu")
-bridge_cpp = os.path.join(script_dir, "ex_engine", "csrc", "ix_full_bridge_v2.cpp")
+# Find source files — try direct csrc/ first, then ex_engine/csrc/
+moe_cu = ""
+bridge_cpp = ""
+for base in [script_dir, os.path.join(script_dir, "ex_engine")]:
+    candidate_cu = os.path.join(base, "csrc", "moe_ops_impl.cu")
+    candidate_cpp = os.path.join(base, "csrc", "ix_full_bridge_v2.cpp")
+    if os.path.isfile(candidate_cu):
+        moe_cu = candidate_cu
+    if os.path.isfile(candidate_cpp):
+        bridge_cpp = candidate_cpp
+if not moe_cu or not bridge_cpp:
+    print(f"[moe_bridge] ERROR: sources not found under {script_dir}")
+    sys.exit(1)
+print(f"[moe_bridge] MOE_CU: {moe_cu}")
+print(f"[moe_bridge] BRIDGE_CPP: {bridge_cpp}")
 
 # Collect linker flags
 extra_ldflags = []