feat(import): Z-wafer CSV import button with result banner

- importZWaferCsv slot on FileBrowser — converts and adds to list
- SourcePanel: import icon button → FileDialog → importSummary banner
  (auto-dismisses after 5s, loads the converted file into streamController)
- wafer_map_item: showExtremes default → true

src/pygui/backend/wafer/zwafer_parser.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from datetime import datetime
 from pathlib import Path
 from typing import Optional, Tuple
@@ -74,6 +76,31 @@ class ZWaferParser:
 
         return wafer_data  # Incomplete file — return partial data
 
+    # ===== Data Row Extraction =====
+    def parse_data_rows(self, file_path: str) -> list[str]:
+        """Return data rows after the 'data' marker, with the leading
+        row-index column stripped (each row realigned to `csv_headers`).
+
+        Uses the same line normalization as `_process_header` so the split
+        point matches exactly what header parsing used.
+        """
+        rows: list[str] = []
+        seen_data_marker = False
+        with Path(file_path).open("r", encoding="utf-8") as f:
+            for raw_line in f:
+                line = raw_line.rstrip().rstrip(",").strip()
+                if not line or line.replace(",", "").strip() == "":
+                    continue
+
+                parts = [p.strip() for p in line.split(",")]
+                if not seen_data_marker:
+                    if parts[0].lower() == "data":
+                        seen_data_marker = True
+                    continue
+
+                rows.append(",".join(parts[1:]))
+        return rows
+
     # ===== Metadata Parsing =====
     def _parse_header_line(self, wafer_data: ZWaferData, parts: list) -> bool:
         """Parse key=value pairs from header line. Returns True if handled."""