fix(gui): high-contrast checkbox indicator

A checked checkbox was hard to distinguish from unchecked on the dark theme.
Style QCheckBox::indicator: accent-filled box with a checkmark when checked,
dark box with a visible border when not.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/rigdoctor/__init__.py

@@ -1,3 +1,3 @@
 """RigDoctor — modular hardware monitoring & crash diagnostics for Linux gamers."""
 
-__version__ = "0.4.0"
+__version__ = "0.4.1"

src/rigdoctor/gui/assets/check.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+  <path d="M3.5 8.5 L6.5 11.5 L12.5 4.5" fill="none" stroke="#06222e"
+        stroke-width="2.4" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>

src/rigdoctor/gui/theme.py

@@ -2,6 +2,10 @@
 
 from __future__ import annotations
 
+from pathlib import Path
+
+_CHECK = (Path(__file__).parent / "assets" / "check.svg").as_posix()
+
 # Palette (dark)
 BG = "#101216"
 SIDEBAR = "#15181e"
@@ -120,6 +124,16 @@ QPushButton#LinkButton {{
 }}
 QPushButton#LinkButton:hover {{ color: {TEXT}; }}
 
+QCheckBox {{ spacing: 8px; background: transparent; }}
+QCheckBox::indicator {{
+    width: 17px; height: 17px; border-radius: 4px;
+    border: 1px solid {MUTED}; background: #262b34;
+}}
+QCheckBox::indicator:hover {{ border-color: {ACCENT}; }}
+QCheckBox::indicator:checked {{
+    background: {ACCENT}; border-color: {ACCENT}; image: url("{_CHECK}");
+}}
+
 /* Dialogs (update prompt, changelog) — match the dark theme so text is readable. */
 QDialog {{ background: {BG}; }}
 QMessageBox {{ background: {CARD}; }}