P5: per-platform transparent, size-appropriate window/tray icons

Give the window titlebar, taskbar, and tray a size-appropriate icon with a
transparent boundary on both Windows and Linux, instead of scaling one PNG to
every size.

Assets:
- Regenerate the PNGs and gosentry.ico with feathered color-to-alpha so the
  rounded-tile boundary is transparent; a binary white-key had left an opaque
  halo that read as a border on dark taskbars/trays.
- Rebuild gosentry.ico as multi-size (16 hand-tuned + 32/48/256 from big) and
  add a single-frame 16x16 gosentry-icon-16x16.ico for the Windows tray.
- assets.go: add IconSmall() and IconSmallICO().

Wiring:
- Windows window/taskbar: embed gosentry.ico under the GLFW_ICON resource and
  skip a.SetIcon so GLFW selects the right frame per size (hand-tuned 16 for the
  titlebar, a larger frame for the taskbar).
- Windows tray: SetSystemTrayIcon(IconSmallICO()), a 16x16 ICO frame.
- Linux window titlebar: a.SetIcon(IconSmall()) for a crisp ~16px _NET_WM_ICON;
  tray uses the big PNG since StatusNotifierItem renders larger.

Also bump Fyne 2.6.3 -> 2.7.4 (systray 1.11.0 -> 1.12.1) and document the full
cross-platform icon strategy in assets.go, gosentry.rc, run.go, and tray.go.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

assets/assets.go

@@ -6,25 +6,87 @@ import (
 	"fyne.io/fyne/v2"
 )
 
-// The application icon is embedded into the binary instead of being loaded from
-// an assets directory at runtime. That keeps the Windows/Linux distribution to a
-// single executable and avoids the common failure mode where the app starts with
-// a generic icon because a sidecar PNG was not copied with the binary.
+// Icons are embedded into the binary instead of being loaded from an assets
+// directory at runtime. That keeps the Windows/Linux distribution to a single
+// executable and avoids the common failure mode where the app starts with a
+// generic icon because a sidecar PNG was not copied with the binary. The blank
+// "embed" import enables the //go:embed directives below.
 //
-// The blank import enables the compiler directive below; no runtime package
-// initialization from embed is required.
+// # Cross-platform icon strategy
 //
+// The hard constraint: Fyne's a.SetIcon and SetSystemTrayIcon each take ONE
+// image, which the OS then scales to every size it needs — titlebar (~16px),
+// taskbar/dock (~32-48px), and tray. Neither source survives that scaling:
+// downscaling the 1254px gosentry-icon-big.png to 16px is muddy, and upscaling
+// the 16px icon to 32px is blurry. The fix is to feed each surface a
+// size-appropriate source — which differs per platform because each platform
+// exposes different icon channels.
+//
+// Source assets (all have a transparent boundary; note that a *binary* white-key
+// leaves the anti-aliased edge fully opaque as a light halo that reads as a
+// border on a dark taskbar/tray, so the background is removed with feathered
+// color-to-alpha instead):
+//   - gosentry-icon-big.png   detailed large artwork (teal rounded-tile emblem)
+//   - gosentry-icon-16x16.png hand-tuned for legibility at 16px
+//   - gosentry.ico            multi-size 16/32/48/256 (16 = the hand-tuned PNG,
+//                             the rest downscaled from big). Embedded into the PE
+//                             binary by windres (see scripts/build-windows.bat),
+//                             NOT via Go embed.
+//   - gosentry-icon-16x16.ico single 16px frame, for the Windows tray
+//
+// Windows:
+//   - Window titlebar + taskbar: the multi-size gosentry.ico, embedded by the .rc
+//     under the resource name GLFW_ICON (packaging/windows/gosentry.rc). GLFW uses
+//     it as the window's default icon and selects the right frame per size — the
+//     hand-tuned 16 for the titlebar, a larger frame for the taskbar. For this to
+//     work, src/ui/run.go must NOT call a.SetIcon on Windows: a single SetIcon
+//     resource overrides GLFW_ICON and would be scaled to both sizes.
+//   - Tray: SetSystemTrayIcon(IconSmallICO()). The notification area is ICO-native
+//     and renders at 16-24px; a single-frame 16x16 .ico pins the hand-tuned glyph
+//     (a multi-size .ico made the tray pick and downscale a larger frame).
+//
+// Linux / other non-Windows (no PE icon resource exists):
+//   - Window titlebar: a.SetIcon(IconSmall()) in run.go feeds the resource to
+//     _NET_WM_ICON, which the window manager renders ~16px in the titlebar, so the
+//     hand-tuned 16x16 keeps it crisp.
+//   - Dock/launcher: the larger icon comes from the .desktop entry's Icon=, written
+//     by InstallDesktopIcon (src/platform/desktop) from the big artwork.
+//   - Tray: SetSystemTrayIcon(Icon()). StatusNotifierItem renders 22-48px and takes
+//     a PNG, so the big artwork scales down cleanly (the 16x16 would look tiny).
+
+//go:embed gosentry-icon-16x16.png
+var iconSmallBytes []byte
+
 //go:embed gosentry-icon-big.png
 var iconBytes []byte
 
+//go:embed gosentry-icon-16x16.ico
+var iconSmallICOBytes []byte
+
+// IconSmall returns the hand-tuned 16x16 PNG. It is the Linux window-titlebar
+// icon (via a.SetIcon -> _NET_WM_ICON, which the WM renders at ~16px). On Windows
+// the titlebar comes from gosentry.ico instead; see the package strategy above.
+func IconSmall() fyne.Resource {
+	return fyne.NewStaticResource("gosentry-icon-16x16.png", iconSmallBytes)
+}
+
+// IconSmallICO returns a single-frame 16x16 Windows .ico of the hand-tuned small
+// icon, used for the Windows system tray. The notification area is ICO-native, and
+// pinning a single 16x16 frame keeps the hand-tuned glyph crisp at tray size — a
+// multi-size .ico lets the tray pick and downscale a larger, muddier frame.
+func IconSmallICO() fyne.Resource {
+	return fyne.NewStaticResource("gosentry-icon-16x16.ico", iconSmallICOBytes)
+}
+
+// Icon returns the large artwork PNG. It is the Linux tray icon (StatusNotifierItem
+// renders 22-48px) and the source for the Linux .desktop dock icon via IconBytes.
+// The Windows window/taskbar icon comes from gosentry.ico, not this resource.
 func Icon() fyne.Resource {
-	// Fyne accepts resources from memory, so the same embedded PNG can be used
-	// for the window icon and tray icon. The Windows Explorer icon is still added
-	// by the build script through the .ico resource, because Explorer reads PE
-	// resources rather than Fyne runtime state.
 	return fyne.NewStaticResource("gosentry-icon-big.png", iconBytes)
 }
 
+// IconBytes is the large artwork as raw PNG bytes for InstallDesktopIcon, which
+// writes the Linux .desktop launcher/dock icon.
 func IconBytes() []byte {
 	return append([]byte(nil), iconBytes...)
 }