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/sql_editor.py

@@ -81,7 +81,7 @@ class CodeEditor(QPlainTextEdit):
         extra = []
         if not self.isReadOnly():
             sel = QTextEdit.ExtraSelection()
-            sel.format.setBackground(QColor("#2a2a3c"))
+            sel.format.setBackground(QColor("#3d4155"))
             sel.format.setProperty(QTextFormat.Property.FullWidthSelection, True)
             sel.cursor = self.textCursor()
             sel.cursor.clearSelection()
@@ -90,7 +90,7 @@ class CodeEditor(QPlainTextEdit):
 
     def line_number_area_paint_event(self, event):
         painter = QPainter(self._line_area)
-        painter.fillRect(event.rect(), QColor("#1a1a2e"))
+        painter.fillRect(event.rect(), QColor("#2a2d3e"))
 
         block  = self.firstVisibleBlock()
         number = block.blockNumber()
@@ -100,7 +100,7 @@ class CodeEditor(QPlainTextEdit):
 
         while block.isValid() and top <= event.rect().bottom():
             if block.isVisible() and bottom >= event.rect().top():
-                painter.setPen(QColor("#45475a"))
+                painter.setPen(QColor("#51576d"))
                 painter.drawText(
                     0, top, self._line_area.width() - 6,
                     self.fontMetrics().height(),
@@ -339,7 +339,7 @@ class FindBar(QWidget):
         self._do_find(backward=True)
 
     def _set_no_match(self, no_match: bool):
-        color = "#f38ba8" if no_match else ""
+        color = "#e78284" if no_match else ""
         self._find_input.setStyleSheet(
             f"background: {color};" if no_match else ""
         )