Add customizable highlight overlay color setting

[JezaChen]

Description

Currently, the highlight overlay color shown when hovering over widgets during inspect mode is hardcoded as rgba(255, 0, 0, 0.2) (red with 20% opacity). This makes it difficult to distinguish the overlay on widgets that already have a red background or similar coloring.

Proposed Solution

Add a configurable highlight overlay color setting in the Settings window:

• A new "Highlight Settings" group box below "IDE Settings" with a color picker button that supports alpha channel
• The selected color is persisted in settings.ini under [Highlight] section
• The color is transmitted to the client (debuggee) process via the existing CMD_ENABLE_INSPECT extra data mechanism
• Cached overlay widgets are refreshed with the latest color on each highlight, so changes take effect without restart

Affected Files

• PyQtInspect/pqi_gui/settings/controller.py — New Highlight/Color setting key
• PyQtInspect/pqi_gui/windows/settings_window.py — New HighlightSettingsGroupBox UI
• PyQtInspect/pqi_server_gui.py — Send color in inspect extra data
• PyQtInspect/pqi.py — highlight_color property on PyDB
• PyQtInspect/_pqi_bundle/pqi_monkey_qt_helpers.py — Dynamic color in overlay rendering