theme: upgrade palette from Catppuccin Mocha to Frappé

Replaces all dark-Mocha colours (#1e1e2e base, #313244 surface0, etc.)
with the noticeably brighter Frappé variants (#303446 base, #414559
surface0, etc.) across the QSS and every hardcoded colour in Python
source files (syntax highlighter, completer popup, log viewer, explain
view, table viewer, schema browser, icons, etc.).

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

app/ui/table_viewer.py

@@ -148,17 +148,17 @@ class EditableTableModel(QAbstractTableModel):
 
         if role == Qt.ItemDataRole.ForegroundRole:
             if self._is_deleted_row(r):
-                return QBrush(QColor("#f38ba8"))   # red — pending delete
+                return QBrush(QColor("#e78284"))   # red — pending delete
             if (r, c) in self._dirty:
-                return QBrush(QColor("#fab387"))   # orange — edited
+                return QBrush(QColor("#ef9f76"))   # orange — edited
             if val is None:
-                return QBrush(QColor("#6c7086"))   # grey — NULL
+                return QBrush(QColor("#737994"))   # grey — NULL
 
         if role == Qt.ItemDataRole.BackgroundRole:
             if self._is_deleted_row(r):
-                return QBrush(QColor("#2a1a1e"))
+                return QBrush(QColor("#3a2530"))
             if (r, c) in self._dirty:
-                return QBrush(QColor("#2a1f1a"))
+                return QBrush(QColor("#3a2f25"))
 
         return None
 
@@ -351,7 +351,7 @@ class TableViewer(QWidget):
 
         # Separator
         sep = QLabel("|")
-        sep.setStyleSheet("color:#45475a; padding:0 4px;")
+        sep.setStyleSheet("color:#51576d; padding:0 4px;")
 
         # CRUD buttons
         self._add_btn    = QPushButton("➕ Add")