[AppColors] Address review comments

- PaletteEditorDialog::onSave(): compare whole PaletteConfig (colors and
  appColors) so a change to only AccentStrong/AccentSoft writes the file;
  add PaletteConfig::operator==.
- appColor(): derive both roles from QPalette::Highlight unconditionally.
  The Fusion palettes pin Accent to near-Window values, and QPalette::Accent
  only exists on Qt 6.6+, so keying on it made identical themes render very
  differently across Qt versions.
- themeChangedSlot(): merge the theme default's [AppColors] into a custom
  palette that predates the section instead of all-or-nothing per file;
  hasPalette() now counts an appColors-only file as a palette.
- Add Default/palette-default-light.toml so the Default theme's Light scheme
  keeps the classic greens instead of falling back to the OS accent.
- home_widget: restore the isBuiltInTheme() half of the Automatic condition;
  non-built-in themes extract button colors from their own background art.
- palette_grid_widget: use appEnum.value(i) for the role cast (3 sites),
  append appHeader to headerLabels, fix the 'Lighted' typo.

cockatrice/themes/Default/palette-default-light.toml

@@ -0,0 +1,67 @@
+[Palette]
+WindowText           = #ff000000
+Button               = #fff0f0f0
+Light                = #ffffffff
+Midlight             = #ffe3e3e3
+Dark                 = #ffa0a0a0
+Mid                  = #ffa0a0a0
+Text                 = #ff000000
+BrightText           = #ffffffff
+ButtonText           = #ff000000
+Base                 = #ffffffff
+Window               = #fff0f0f0
+Shadow               = #ff696969
+HighlightedText      = #ffffffff
+Link                 = #ff0d5f28
+LinkVisited          = #ff08401b
+AlternateBase        = #ffe9e7e3
+ToolTipBase          = #ffffffdc
+ToolTipText          = #ff000000
+PlaceholderText      = #80000000
+
+[Palette.Disabled]
+WindowText           = #ff787878
+Button               = #fff0f0f0
+Light                = #ffffffff
+Midlight             = #fff7f7f7
+Dark                 = #ffa0a0a0
+Mid                  = #ffa0a0a0
+Text                 = #ff787878
+BrightText           = #ffffffff
+ButtonText           = #ff787878
+Base                 = #fff0f0f0
+Window               = #fff0f0f0
+Shadow               = #ff000000
+HighlightedText      = #ffffffff
+Link                 = #ff0000ff
+LinkVisited          = #ffff00ff
+AlternateBase        = #fff7f7f7
+ToolTipBase          = #ffffffdc
+ToolTipText          = #ff000000
+PlaceholderText      = #80000000
+
+[Palette.Inactive]
+WindowText           = #ff000000
+Button               = #fff0f0f0
+Light                = #ffffffff
+Midlight             = #ffe3e3e3
+Dark                 = #ffa0a0a0
+Mid                  = #ffa0a0a0
+Text                 = #ff000000
+BrightText           = #ffffffff
+ButtonText           = #ff000000
+Base                 = #ffffffff
+Window               = #fff0f0f0
+Shadow               = #ff696969
+HighlightedText      = #ff000000
+Link                 = #ff0d5f28
+LinkVisited          = #ff08401b
+AlternateBase        = #ffe9e7e3
+ToolTipBase          = #ffffffdc
+ToolTipText          = #ff000000
+PlaceholderText      = #80000000
+
+
+[AppColors]
+AccentStrong        = #ff148c3c
+AccentSoft          = #ff78c850