feat: add tray streaming status and app icon

- tray icon and tooltip now reflect engine state: grey when stopped,
  green + live frame/drop counters in the tooltip while streaming
- generate a proper app icon (assets/, via cmd/teleportfling-icon) and
  embed it so the window and tray carry the icon without runtime files
- add a .desktop entry template for launching from an app menu
- run Fyne UI updates (status label, tray icon/tooltip) on the main
  thread via fyne.Do to satisfy the threading model

internal/gui/gui.go

@@ -8,6 +8,7 @@ package gui
 
 import (
 	"errors"
+	"image/color"
 	"log"
 	"strconv"
 	"time"
@@ -18,7 +19,9 @@ import (
 	"fyne.io/fyne/v2/dialog"
 	"fyne.io/fyne/v2/driver/desktop"
 	"fyne.io/fyne/v2/widget"
+	"fyne.io/systray"
 
+	"teleportfling/assets"
 	"teleportfling/internal/config"
 	"teleportfling/internal/flinger"
 )
@@ -38,11 +41,15 @@ const appID = "io.teleportfling"
 type App struct {
 	fyneApp fyne.App
 	win     fyne.Window
+	desk    desktop.App
 
 	cfg  config.Config
 	eng  *flinger.Engine
 	lock bool // serialises start/stop against UI actions
 
+	// Tray state icons, built once at startup.
+	iconIdle, iconActive *staticResource
+
 	// UI state.
 	startBtn    *widget.Button
 	statusLab   *widget.Label
@@ -62,6 +69,9 @@ func Run() {
 
 	g.fyneApp = app.NewWithID(appID)
 	g.win = g.fyneApp.NewWindow("TeleportFling")
+	g.fyneApp.SetIcon(fyne.NewStaticResource("teleportfling", assets.AppIcon))
+	g.iconIdle = newTrayResource(color.NRGBA{R: 90, G: 90, B: 95, A: 255}, color.NRGBA{R: 60, G: 60, B: 65, A: 255})
+	g.iconActive = newTrayResource(color.NRGBA{R: 46, G: 125, B: 50, A: 255}, color.NRGBA{R: 150, G: 220, B: 140, A: 255})
 
 	// Load persisted settings (falling back to defaults).
 	g.cfg = mustLoadConfig()
@@ -207,6 +217,7 @@ func (g *App) start() {
 	g.startBtn.Importance = widget.DangerImportance
 	g.statusLab.SetText("Streaming (port " + itoa(g.cfg.Port) + ")")
 	g.statusLab.Importance = widget.SuccessImportance
+	g.setTrayState(true, "TeleportFling · Streaming")
 	g.refresh()
 	g.watchStats()
 }
@@ -225,7 +236,13 @@ func (g *App) watchStats() {
 					return
 				}
 				st := g.eng.Status()
-				g.statusLab.SetText(formatStatus(st))
+				frames := itoa(int(st.Frames))
+				dropped := itoa(int(st.Dropped))
+				// Fyne UI calls must run on the main thread.
+				fyne.Do(func() {
+					g.statusLab.SetText(formatStatus(st))
+					g.setTrayState(true, "TeleportFling · "+frames+" frames, "+dropped+" dropped")
+				})
 			case <-done:
 				return
 			}
@@ -256,6 +273,7 @@ func (g *App) stop() {
 	g.startBtn.Importance = widget.HighImportance
 	g.statusLab.SetText("Stopped")
 	g.statusLab.Importance = widget.MediumImportance
+	g.setTrayState(false, "TeleportFling")
 	g.refresh()
 }
 
@@ -274,6 +292,7 @@ func (g *App) setupTray() {
 		log.Printf("gui: system tray not supported on this desktop")
 		return
 	}
+	g.desk = desk
 
 	m := fyne.NewMenu("TeleportFling",
 		fyne.NewMenuItem("Show", func() {
@@ -301,4 +320,21 @@ func (g *App) setupTray() {
 	// Left-clicking the tray icon shows the settings window.
 	desk.SetSystemTrayWindow(g.win)
 	g.win.SetOnClosed(func() { g.fyneApp.Quit() })
+
+	// Show the "stopped" state icon initially.
+	g.setTrayState(false, "TeleportFling")
+}
+
+// setTrayState swaps the tray icon and tooltip to reflect the streaming state.
+// It is a no-op if the tray is unavailable.
+func (g *App) setTrayState(streaming bool, tooltip string) {
+	if g.desk == nil || g.iconIdle == nil || g.iconActive == nil {
+		return
+	}
+	icon := fyne.Resource(g.iconIdle)
+	if streaming {
+		icon = g.iconActive
+	}
+	g.desk.SetSystemTrayIcon(icon)
+	systray.SetTooltip(tooltip)
 }

internal/gui/icon.go

@@ -0,0 +1,83 @@
+// Package gui provides the Fyne desktop app: a settings window and a system
+// tray that start/stop the flinger engine.
+//
+// The engine itself lives in internal/flinger and is GUI-free, so the tray
+// can control streaming without any UI dependency. This package wires the two
+// together: config persistence, the settings form, the tray menu and the
+// tray status icon.
+package gui
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/png"
+)
+
+// traySize is the icon size in pixels. Tray hosts typically request 22px;
+// we render larger and let the host scale down for crispness.
+const traySize = 64
+
+// newTrayResource renders a rounded square with a status dot into a
+// fyne.Resource that SetSystemTrayIcon accepts.
+func newTrayResource(bg, dot color.NRGBA) *staticResource {
+	img := image.NewRGBA(image.Rect(0, 0, traySize, traySize))
+
+	// Rounded-square background.
+	radius := 14
+	for y := 0; y < traySize; y++ {
+		for x := 0; x < traySize; x++ {
+			if inRoundedRect(x, y, radius) {
+				img.Set(x, y, bg)
+			}
+		}
+	}
+
+	// Center status dot.
+	cx, cy, r := traySize/2, traySize/2, 16
+	for y := cy - r; y <= cy+r; y++ {
+		for x := cx - r; x <= cx+r; x++ {
+			if (x-cx)*(x-cx)+(y-cy)*(y-cy) <= r*r {
+				img.Set(x, y, dot)
+			}
+		}
+	}
+
+	var buf bytes.Buffer
+	_ = png.Encode(&buf, img)
+	return &staticResource{name: "teleportfling-tray", data: buf.Bytes()}
+}
+
+// inRoundedRect reports whether (x,y) falls inside the rounded square.
+func inRoundedRect(x, y, radius int) bool {
+	const m = traySize - 1
+	switch {
+	case x >= radius && x <= m-radius:
+		return true
+	case y >= radius && y <= m-radius:
+		return true
+	}
+	// Corner: within radius of the nearest corner centre.
+	var cx, cy int
+	if x < radius {
+		cx = radius
+	} else {
+		cx = m - radius
+	}
+	if y < radius {
+		cy = radius
+	} else {
+		cy = m - radius
+	}
+	dx, dy := x-cx, y-cy
+	return dx*dx+dy*dy <= radius*radius
+}
+
+// staticResource is a simple in-memory fyne.Resource.
+type staticResource struct {
+	name string
+	data []byte
+}
+
+func (r *staticResource) Name() string    { return r.name }
+func (r *staticResource) Content() []byte { return r.data }