feat: multi-result tabs, column statistics, and Ctrl+W close tab

- ResultsPanel rewritten: single queries show one result as before;
  scripts with multiple statements show each result in a named sub-tab
  (e.g. "Result 2 (1,234)") with the tab bar auto-shown/hidden
- EditorTab._on_script_done now calls show_script_results() instead of
  overwriting the panel on each statement
- ColumnStatsDialog: right-click any column header in TableViewer to see
  total rows, null count, distinct values, min, max, and avg (async,
  gracefully skips avg for non-numeric columns)
- TableViewer header context menu also adds "Resize to fit" shortcuts
- Ctrl+W closes the current workspace tab (View menu)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/ui/column_stats_dialog.py

@@ -0,0 +1,134 @@
+"""Column statistics dialog — shows row count, nulls, distinct, min, max, avg."""
+from PyQt6.QtWidgets import (
+    QDialog, QVBoxLayout, QFormLayout, QLabel, QDialogButtonBox,
+    QGroupBox, QProgressBar, QSizePolicy,
+)
+from PyQt6.QtCore import Qt, QThread, pyqtSignal
+from PyQt6.QtGui import QFont
+
+
+class _StatsWorker(QThread):
+    result  = pyqtSignal(dict)
+    error   = pyqtSignal(str)
+
+    def __init__(self, driver, database: str, table: str, column: str):
+        super().__init__()
+        self._driver   = driver
+        self._database = database
+        self._table    = table
+        self._column   = column
+
+    def run(self):
+        col  = self._column
+        tbl  = self._table
+        try:
+            _, rows, _ = self._driver.execute_query(
+                f'SELECT COUNT(*), COUNT("{col}"), COUNT(DISTINCT "{col}"), '
+                f'MIN("{col}"), MAX("{col}") FROM "{tbl}"'
+            )
+            total, non_null, distinct, min_val, max_val = rows[0]
+            null_count = (total or 0) - (non_null or 0)
+        except Exception as e:
+            self.error.emit(str(e))
+            return
+
+        avg_val = None
+        try:
+            _, avg_rows, _ = self._driver.execute_query(
+                f'SELECT AVG("{col}") FROM "{tbl}"'
+            )
+            avg_val = avg_rows[0][0]
+        except Exception:
+            pass
+
+        self.result.emit({
+            "total":    total,
+            "non_null": non_null,
+            "nulls":    null_count,
+            "distinct": distinct,
+            "min":      min_val,
+            "max":      max_val,
+            "avg":      avg_val,
+        })
+
+
+class ColumnStatsDialog(QDialog):
+    def __init__(self, driver, database: str, table: str, column: str, parent=None):
+        super().__init__(parent)
+        self.setWindowTitle(f"Column Statistics — {column}")
+        self.setMinimumWidth(360)
+        self._driver   = driver
+        self._database = database
+        self._table    = table
+        self._column   = column
+        self._build_ui()
+        self._load()
+
+    def _build_ui(self):
+        root = QVBoxLayout(self)
+        root.setSpacing(10)
+        root.setContentsMargins(16, 16, 16, 16)
+
+        subtitle = QLabel(f"<b>{self._table}</b>.<i>{self._column}</i>")
+        subtitle.setTextFormat(Qt.TextFormat.RichText)
+        root.addWidget(subtitle)
+
+        # ── Stats group ───────────────────────────────────────────────────────
+        box = QGroupBox("Statistics")
+        self._form = QFormLayout(box)
+        self._form.setSpacing(6)
+        self._rows: dict[str, QLabel] = {}
+        for key, label in [
+            ("total",    "Total rows"),
+            ("non_null", "Non-null"),
+            ("nulls",    "Null count"),
+            ("distinct", "Distinct values"),
+            ("min",      "Min"),
+            ("max",      "Max"),
+            ("avg",      "Avg (numeric)"),
+        ]:
+            lbl = QLabel("…")
+            lbl.setFont(QFont("Consolas", 10))
+            self._form.addRow(label + ":", lbl)
+            self._rows[key] = lbl
+        root.addWidget(box)
+
+        # ── Loading bar ───────────────────────────────────────────────────────
+        self._progress = QProgressBar()
+        self._progress.setMaximum(0)
+        self._progress.setFixedHeight(6)
+        self._progress.setTextVisible(False)
+        root.addWidget(self._progress)
+
+        bb = QDialogButtonBox(QDialogButtonBox.StandardButton.Close)
+        bb.rejected.connect(self.reject)
+        root.addWidget(bb)
+
+    def _load(self):
+        self._worker = _StatsWorker(
+            self._driver, self._database, self._table, self._column
+        )
+        self._worker.result.connect(self._on_result)
+        self._worker.error.connect(self._on_error)
+        self._worker.finished.connect(self._progress.hide)
+        self._worker.start()
+
+    def _on_result(self, stats: dict):
+        for key, lbl in self._rows.items():
+            val = stats.get(key)
+            if val is None:
+                text = "N/A"
+            elif isinstance(val, float):
+                text = f"{val:,.4f}"
+            else:
+                try:
+                    text = f"{int(val):,}"
+                except (TypeError, ValueError):
+                    text = str(val)
+            lbl.setText(text)
+
+    def _on_error(self, msg: str):
+        for lbl in self._rows.values():
+            lbl.setText("—")
+        self._rows["total"].setText(f"Error: {msg[:60]}")
+        self._rows["total"].setStyleSheet("color: #e78284;")