Add shield icon: medieval round shield with Syncthing motif warpaint

Redesign tray/app icon as a wooden round shield with iron rim, rivets,
wood grain, and the Syncthing network motif (ring + 3 nodes + spokes)
painted in the state color. Dark shadow outline for wood contrast.
Inspired by Stammtisch hero icon style (warm, illustrated wood tones).

- Dynamic tray icon changes color per state (green/blue/gray/red)
- Static assets: PNG at 7 sizes + multi-size .ico + preview sheet
- Icon generator utility (cmd/icongen)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/icons/render.go

@@ -3,6 +3,7 @@ package icons
 import (
 	"bytes"
 	"encoding/binary"
+	"image/color"
 	"image/png"
 	"math"
 	"runtime"
@@ -15,8 +16,13 @@ const iconSize = 64
 // Render generates a tray icon for the given state.
 // Returns ICO bytes on Windows, PNG bytes on other platforms.
 func Render(state State) ([]byte, error) {
-	dc := gg.NewContext(iconSize, iconSize)
-	drawSyncIcon(dc, state)
+	return RenderSize(state, iconSize)
+}
+
+// RenderSize generates an icon at the given pixel size.
+func RenderSize(state State, size int) ([]byte, error) {
+	dc := gg.NewContext(size, size)
+	drawShieldIcon(dc, state, float64(size))
 
 	var buf bytes.Buffer
 	if err := png.Encode(&buf, dc.Image()); err != nil {
@@ -25,53 +31,212 @@ func Render(state State) ([]byte, error) {
 
 	pngData := buf.Bytes()
 	if runtime.GOOS == "windows" {
-		return wrapPNGInICO(pngData, iconSize, iconSize), nil
+		return wrapPNGInICO(pngData, size, size), nil
 	}
 	return pngData, nil
 }
 
-// drawSyncIcon draws a circular sync arrows icon in the state's color.
-func drawSyncIcon(dc *gg.Context, state State) {
-	c := colorForState(state)
-	cx := float64(iconSize) / 2
-	cy := float64(iconSize) / 2
-	radius := float64(iconSize)*0.35
-	arrowWidth := 5.0
+// RenderPNG generates a PNG icon at the given size, regardless of platform.
+func RenderPNG(state State, size int) ([]byte, error) {
+	dc := gg.NewContext(size, size)
+	drawShieldIcon(dc, state, float64(size))
 
-	dc.SetColor(c)
-	dc.SetLineWidth(arrowWidth)
-	dc.SetLineCap(gg.LineCapRound)
-
-	// Draw two circular arcs (sync arrows)
-	// Top arc: from 220° to 320°
-	drawArcWithArrow(dc, cx, cy, radius, degToRad(220), degToRad(320), arrowWidth)
-	// Bottom arc: from 40° to 140°
-	drawArcWithArrow(dc, cx, cy, radius, degToRad(40), degToRad(140), arrowWidth)
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, dc.Image()); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
 }
 
-func drawArcWithArrow(dc *gg.Context, cx, cy, radius, startAngle, endAngle, lineWidth float64) {
-	// Draw the arc
-	dc.DrawArc(cx, cy, radius, startAngle, endAngle)
+// Shield color palette — warm wood tones inspired by Stammtisch
+var (
+	shieldRim   = color.RGBA{55, 42, 30, 255}     // dark iron rim
+	shieldOuter = color.RGBA{130, 82, 38, 255}    // darker wood ring
+	shieldMid   = color.RGBA{175, 118, 58, 255}   // warm wood body
+	shieldInner = color.RGBA{195, 140, 72, 255}   // lighter wood center
+	shieldLight = color.RGBA{210, 162, 95, 255}   // highlight zone
+	grainDark   = color.RGBA{145, 90, 40, 200}    // wood grain shadow
+	rivetBody   = color.RGBA{105, 95, 80, 255}    // iron rivet
+	rivetShine  = color.RGBA{160, 150, 130, 255}  // rivet highlight
+	bossEdge    = color.RGBA{80, 65, 45, 255}     // boss rim
+	bossBody    = color.RGBA{145, 130, 105, 255}  // boss metal
+	bossShine   = color.RGBA{190, 180, 160, 255}  // boss highlight
+	motifShadow = color.RGBA{40, 30, 20, 100}     // dark outline behind motif
+)
+
+func drawShieldIcon(dc *gg.Context, state State, s float64) {
+	cx := s / 2
+	cy := s / 2
+	sc := s / 64 // scale factor relative to 64px base
+
+	// 1. Shield rim (dark outer ring)
+	rimR := s * 0.47
+	dc.DrawCircle(cx, cy, rimR)
+	dc.SetColor(shieldRim)
+	dc.Fill()
+
+	// 2. Shield face — layered wood rings
+	faceR := s * 0.42
+	drawWoodFace(dc, cx, cy, faceR)
+
+	// 3. Wood grain arcs (skip at very small sizes)
+	if s >= 48 {
+		drawWoodGrain(dc, cx, cy, faceR, sc)
+	}
+
+	// 4. Rivets around rim (skip below 32px)
+	if s >= 32 {
+		rivetCount := 12
+		if s < 48 {
+			rivetCount = 8
+		}
+		drawRivets(dc, cx, cy, rimR-2*sc, sc, rivetCount)
+	}
+
+	// 5. Syncthing motif — "warpaint" in state color
+	drawSyncthingMotif(dc, cx, cy, faceR, state, sc)
+
+	// 6. Center boss
+	drawBoss(dc, cx, cy, sc)
+}
+
+func drawWoodFace(dc *gg.Context, cx, cy, r float64) {
+	layers := []struct {
+		frac float64
+		c    color.RGBA
+	}{
+		{1.00, shieldOuter},
+		{0.90, shieldMid},
+		{0.72, shieldInner},
+		{0.48, shieldLight},
+		{0.30, shieldInner},
+	}
+	for _, l := range layers {
+		dc.DrawCircle(cx, cy, r*l.frac)
+		dc.SetColor(l.c)
+		dc.Fill()
+	}
+}
+
+func drawWoodGrain(dc *gg.Context, cx, cy, r, sc float64) {
+	dc.SetColor(grainDark)
+	dc.SetLineWidth(math.Max(0.8, 0.7*sc))
+	dc.SetLineCap(gg.LineCapRound)
+
+	arcs := []struct{ radius, startDeg, sweepDeg float64 }{
+		{0.83, 25, 55},
+		{0.83, 195, 50},
+		{0.62, 95, 65},
+		{0.62, 275, 50},
+		{0.42, 5, 75},
+		{0.42, 165, 60},
+	}
+	for _, a := range arcs {
+		dc.DrawArc(cx, cy, r*a.radius, degToRad(a.startDeg), degToRad(a.startDeg+a.sweepDeg))
+		dc.Stroke()
+	}
+}
+
+func drawRivets(dc *gg.Context, cx, cy, r, sc float64, count int) {
+	rr := math.Max(1.2, 1.8*sc) // rivet radius
+
+	for i := 0; i < count; i++ {
+		a := float64(i) * 2 * math.Pi / float64(count)
+		rx := cx + r*math.Cos(a)
+		ry := cy + r*math.Sin(a)
+
+		dc.DrawCircle(rx, ry, rr)
+		dc.SetColor(rivetBody)
+		dc.Fill()
+
+		// Highlight
+		if sc >= 1.0 {
+			dc.DrawCircle(rx-rr*0.2, ry-rr*0.3, rr*0.45)
+			dc.SetColor(rivetShine)
+			dc.Fill()
+		}
+	}
+}
+
+func drawSyncthingMotif(dc *gg.Context, cx, cy, faceR float64, state State, sc float64) {
+	stateCol := colorForState(state)
+	ringR := faceR * 0.58
+	lineW := math.Max(1.8, 2.8*sc)
+	nodeR := math.Max(2.2, 3.2*sc)
+
+	// Node positions: top, bottom-left, bottom-right
+	nodeAngles := []float64{-90, 150, 30}
+	nodes := make([][2]float64, 3)
+	for i, deg := range nodeAngles {
+		rad := degToRad(deg)
+		nodes[i] = [2]float64{
+			cx + ringR*math.Cos(rad),
+			cy + ringR*math.Sin(rad),
+		}
+	}
+
+	// --- Shadow layer (dark outline behind everything for contrast) ---
+	shadowOff := math.Max(0.5, 0.8*sc)
+	dc.SetColor(motifShadow)
+	dc.SetLineWidth(lineW + 2*shadowOff)
+	dc.SetLineCap(gg.LineCapRound)
+
+	// Shadow ring
+	dc.DrawCircle(cx, cy, ringR)
 	dc.Stroke()
 
-	// Draw arrowhead at the end of the arc
-	endX := cx + radius*math.Cos(endAngle)
-	endY := cy + radius*math.Sin(endAngle)
-
-	// Arrow direction is tangent to the circle at the endpoint
-	tangentAngle := endAngle + math.Pi/2
-	arrowLen := lineWidth * 2.5
-
-	// Two points of the arrowhead
-	a1x := endX + arrowLen*math.Cos(tangentAngle+0.5)
-	a1y := endY + arrowLen*math.Sin(tangentAngle+0.5)
-	a2x := endX + arrowLen*math.Cos(tangentAngle-0.5)
-	a2y := endY + arrowLen*math.Sin(tangentAngle-0.5)
-
-	dc.MoveTo(a1x, a1y)
-	dc.LineTo(endX, endY)
-	dc.LineTo(a2x, a2y)
+	// Shadow spokes
+	for _, n := range nodes {
+		dc.DrawLine(cx, cy, n[0], n[1])
+	}
 	dc.Stroke()
+
+	// Shadow nodes
+	for _, n := range nodes {
+		dc.DrawCircle(n[0], n[1], nodeR+shadowOff)
+		dc.Fill()
+	}
+
+	// --- Motif layer (state-colored) ---
+	dc.SetColor(stateCol)
+	dc.SetLineWidth(lineW)
+	dc.SetLineCap(gg.LineCapRound)
+
+	// Ring
+	dc.DrawCircle(cx, cy, ringR)
+	dc.Stroke()
+
+	// Spokes from center to nodes
+	for _, n := range nodes {
+		dc.DrawLine(cx, cy, n[0], n[1])
+	}
+	dc.Stroke()
+
+	// Node circles
+	for _, n := range nodes {
+		dc.DrawCircle(n[0], n[1], nodeR)
+		dc.SetColor(stateCol)
+		dc.Fill()
+	}
+}
+
+func drawBoss(dc *gg.Context, cx, cy, sc float64) {
+	br := math.Max(2.5, 4.5*sc)
+
+	// Edge ring
+	dc.DrawCircle(cx, cy, br+0.8*sc)
+	dc.SetColor(bossEdge)
+	dc.Fill()
+
+	// Body
+	dc.DrawCircle(cx, cy, br)
+	dc.SetColor(bossBody)
+	dc.Fill()
+
+	// Highlight (upper-left)
+	dc.DrawCircle(cx-br*0.22, cy-br*0.28, br*0.5)
+	dc.SetColor(bossShine)
+	dc.Fill()
 }
 
 func degToRad(deg float64) float64 {