refactor(mcp_client): obliterate legacy _resolve_and_check wrapper; migrate 5 callers to _resolve_and_check_result (Phase 3)

Phase 3 (1 of 9 cruft sites obliterated):

The legacy wrapper _resolve_and_check(raw_path) returned tuple[Path|None, str],
dropping the structured ErrorInfo from _resolve_and_check_result. Callers in
dispatch_tool_call (py_remove_def, py_add_def, py_move_def, py_region_wrap) used
the pattern 'p, err = _resolve_and_check(path); if err: return err' which is
exactly the false drain the user wants obliterated.

Migration:
- DELETED: _resolve_and_check wrapper (lines 175-188 in src/mcp_client.py)
- UPDATED: 5 callers in dispatch_tool_call now call _resolve_and_check_result
  directly with .ok check + NilPath check + structured error routing
- UPDATED: 4 test files that monkey-patched _resolve_and_check to mock the
  Result helper instead:
  - test_mcp_ts_integration.py (1 mock)
  - test_ts_c_tools.py (2 mocks)
  - test_ts_cpp_tools.py (8 mocks)
  - test_cruft_removal.py (NEW; 4 tests including the wrapper-obliterated
    invariant + the audit-script-finds-zero invariant + 2 dispatch tests)

Test result: 51/51 pass (31 baseline + 16 heuristic + 4 cruft).
Audit gate: src/mcp_client.py --strict exits 0 (no new violations introduced).
Baseline audit: --include-baseline --strict exits 1 only due to 4 pre-existing
non-baseline INTERNAL_RETHROW sites in outline_tool.py / warmup.py /
vendor_capabilities.py (out of scope per spec).

The wrapper IS DELETED. No pass-through. No backward compat. The dead code dies.

tests/test_ts_c_tools.py

@@ -29,8 +29,8 @@ struct Point {
  
  # Mock _resolve_and_check to allow tmp_path
  from src import mcp_client
- original_resolve = mcp_client._resolve_and_check
- mcp_client._resolve_and_check = lambda path: (Path(path), None)
+ original_resolve = mcp_client._resolve_and_check_result
+ mcp_client._resolve_and_check_result = lambda path: __import__("src").mcp_client.Result(data=Path(path), errors=[])
  
  try:
   skeleton = ts_c_get_skeleton(str(c_file))
@@ -39,7 +39,7 @@ struct Point {
   assert "struct Point" in skeleton
   assert "printf" not in skeleton
  finally:
-  mcp_client._resolve_and_check = original_resolve
+  mcp_client._resolve_and_check_result = original_resolve
 
 def test_ts_c_get_code_outline(tmp_path):
  c_code = """
@@ -54,12 +54,12 @@ int func2(int x) {
  c_file.write_text(c_code)
  
  from src import mcp_client
- original_resolve = mcp_client._resolve_and_check
- mcp_client._resolve_and_check = lambda path: (Path(path), None)
+ original_resolve = mcp_client._resolve_and_check_result
+ mcp_client._resolve_and_check_result = lambda path: __import__("src").mcp_client.Result(data=Path(path), errors=[])
  
  try:
   outline = ts_c_get_code_outline(str(c_file))
   assert "[Func] func1 (Lines 2-3)" in outline
   assert "[Func] func2 (Lines 5-7)" in outline
  finally:
-  mcp_client._resolve_and_check = original_resolve
+  mcp_client._resolve_and_check_result = original_resolve