feat(gui): sidebar nav icons matching the app icon (#19)

## Summary
Give the sidebar nav items (Download · Organize · Settings) icons drawn
in the **same visual language as the app icon** — a rounded-square
"chip" silhouette in Apple-blue with rounded strokes.

- New `gui/ui/icons.py`: programmatic QPainter glyphs (down-arrow +
tray, 2×2 nodes, sliders), rendered at 2× for HiDPI. Accent blue is
identical in both palettes, so they match the app icon and look correct
on dark **and** light themes with no per-theme recolor.
- Wired into `main_window` sidebar; also set the window/dock icon from
`app.icns`.

## Verification
- `ruff check src/gui` clean; dev launch warning-free.
- Rendered both-theme preview confirms legibility and app-icon
consistency.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: subkoks

src/gui/app.py

@@ -21,14 +21,16 @@
     sys.path.insert(0, str(_SRC))
 
 import qasync  # noqa: E402
-from PySide6.QtGui import QFontDatabase  # noqa: E402
+from PySide6.QtGui import QFontDatabase, QIcon  # noqa: E402
 from PySide6.QtWidgets import QApplication  # noqa: E402
 
 from gui.core import paths  # noqa: E402
 from gui.core.settings import APP_NAME, Settings  # noqa: E402
 from gui.ui.main_window import MainWindow  # noqa: E402
 from gui.ui.theme import ThemeManager  # noqa: E402
 
+_ICON_FILE = Path(__file__).resolve().parent / "resources" / "app.icns"
+
 
 def main() -> None:
     app = QApplication(sys.argv)
@@ -38,6 +40,8 @@ def main() -> None:
 
     # Use the real OS UI font (avoids a missing -apple-system family lookup).
     app.setFont(QFontDatabase.systemFont(QFontDatabase.SystemFont.GeneralFont))
+    if _ICON_FILE.exists():
+        app.setWindowIcon(QIcon(str(_ICON_FILE)))
 
     settings = Settings.load()
     paths.apply(settings)

src/gui/ui/icons.py

@@ -0,0 +1,100 @@
+"""Programmatic sidebar icons drawn in the app-icon language.
+
+Each glyph sits inside the same rounded-square "chip" silhouette as the app icon, in
+Apple-blue, with rounded strokes and small pad dots echoing the icon's traces. Rendered
+at 2x for crisp HiDPI. Accent blue is identical in both themes, so icons match the app
+icon and need no per-theme recolor.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+
+from PySide6.QtCore import QPointF, QRectF, Qt
+from PySide6.QtGui import QColor, QIcon, QPainter, QPen, QPixmap
+
+ACCENT = "#2f6df6"
+_SCALE = 2
+
+
+def _pixmap(size: int, draw: Callable[[QPainter, float, QColor], None], color: str) -> QPixmap:
+    pm = QPixmap(size * _SCALE, size * _SCALE)
+    pm.fill(Qt.GlobalColor.transparent)
+    p = QPainter(pm)
+    p.setRenderHint(QPainter.RenderHint.Antialiasing, True)
+    qcolor = QColor(color)
+    pen = QPen(qcolor, 1.7 * _SCALE)
+    pen.setCapStyle(Qt.PenCapStyle.RoundCap)
+    pen.setJoinStyle(Qt.PenJoinStyle.RoundJoin)
+    p.setPen(pen)
+    draw(p, size * _SCALE, qcolor)
+    p.end()
+    pm.setDevicePixelRatio(_SCALE)
+    return pm
+
+
+def _chip(p: QPainter, s: float) -> QRectF:
+    """The shared rounded-square silhouette + two pad dots, like the app icon."""
+    m = s * 0.10
+    rect = QRectF(m, m, s - 2 * m, s - 2 * m)
+    p.setBrush(Qt.BrushStyle.NoBrush)
+    p.drawRoundedRect(rect, s * 0.24, s * 0.24)
+    return rect
+
+
+def _draw_download(p: QPainter, s: float, c: QColor) -> None:
+    r = _chip(p, s)
+    cx = r.center().x()
+    top = r.top() + r.height() * 0.22
+    mid = r.top() + r.height() * 0.52
+    # shaft
+    p.drawLine(QPointF(cx, top), QPointF(cx, mid))
+    # arrow head
+    a = r.width() * 0.16
+    p.drawLine(QPointF(cx - a, mid - a), QPointF(cx, mid))
+    p.drawLine(QPointF(cx + a, mid - a), QPointF(cx, mid))
+    # tray
+    by = r.bottom() - r.height() * 0.22
+    p.drawLine(QPointF(r.left() + r.width() * 0.28, by), QPointF(r.right() - r.width() * 0.28, by))
+
+
+def _draw_organize(p: QPainter, s: float, c: QColor) -> None:
+    r = _chip(p, s)
+    p.setBrush(c)
+    dot = r.width() * 0.075
+    xs = (r.left() + r.width() * 0.36, r.left() + r.width() * 0.64)
+    ys = (r.top() + r.height() * 0.36, r.top() + r.height() * 0.64)
+    for x in xs:
+        for y in ys:
+            p.drawEllipse(QPointF(x, y), dot, dot)
+    p.setBrush(Qt.BrushStyle.NoBrush)
+
+
+def _draw_settings(p: QPainter, s: float, c: QColor) -> None:
+    r = _chip(p, s)
+    knob = r.width() * 0.075
+    rows = (0.34, 0.5, 0.66)
+    knob_x = (0.62, 0.40, 0.58)
+    for row, kx in zip(rows, knob_x, strict=True):
+        y = r.top() + r.height() * row
+        p.setBrush(Qt.BrushStyle.NoBrush)
+        p.drawLine(
+            QPointF(r.left() + r.width() * 0.26, y), QPointF(r.right() - r.width() * 0.26, y)
+        )
+        p.setBrush(c)
+        p.drawEllipse(QPointF(r.left() + r.width() * kx, y), knob, knob)
+    p.setBrush(Qt.BrushStyle.NoBrush)
+
+
+_GLYPHS: dict[str, Callable[[QPainter, float, QColor], None]] = {
+    "download": _draw_download,
+    "organize": _draw_organize,
+    "settings": _draw_settings,
+}
+
+
+def nav_icon(name: str, size: int = 18, color: str = ACCENT) -> QIcon:
+    draw = _GLYPHS.get(name)
+    if draw is None:
+        return QIcon()
+    return QIcon(_pixmap(size, draw, color))

src/gui/ui/main_window.py

@@ -4,7 +4,7 @@
 
 import asyncio
 
-from PySide6.QtCore import QUrl
+from PySide6.QtCore import QSize, QUrl
 from PySide6.QtGui import QDesktopServices
 from PySide6.QtWidgets import (
     QButtonGroup,
@@ -24,6 +24,7 @@
 from ..core.config import get_credentials, load_config
 from ..core.settings import Settings
 from .download_view import DownloadView
+from .icons import nav_icon
 from .login_dialog import LoginCancelled, LoginDialog
 from .organize_view import OrganizeView
 from .settings_dialog import SettingsDialog
@@ -78,13 +79,18 @@ def _build_sidebar(self) -> QWidget:
         layout.addWidget(subtitle)
         layout.addSpacing(10)
 
+        nav_icon_size = QSize(18, 18)
         self._nav_group = QButtonGroup(self)
         self._nav_group.setExclusive(True)
-        for index, label in enumerate(("Download", "Organize")):
+        for index, (label, glyph) in enumerate(
+            (("Download", "download"), ("Organize", "organize"))
+        ):
             btn = QPushButton(label)
             btn.setObjectName("NavButton")
             btn.setCheckable(True)
             btn.setChecked(index == 0)
+            btn.setIcon(nav_icon(glyph))
+            btn.setIconSize(nav_icon_size)
             btn.clicked.connect(lambda _=False, i=index: self._stack.setCurrentIndex(i))
             self._nav_group.addButton(btn, index)
             layout.addWidget(btn)
@@ -93,6 +99,8 @@ def _build_sidebar(self) -> QWidget:
 
         settings_btn = QPushButton("Settings")
         settings_btn.setObjectName("NavButton")
+        settings_btn.setIcon(nav_icon("settings"))
+        settings_btn.setIconSize(nav_icon_size)
         settings_btn.clicked.connect(self._open_settings)
         layout.addWidget(settings_btn)
         return bar