feat(tray): desktop tray icon companion with Theta logo, color-coded status, and home LAN detection (#10)

- tray_icons.go / cmd/theta-agent-tray: Renders iconic Theta 42 logo in status colors:
    - 🔴 Red: Not connected to directory
    - 🟡 Yellow: Connected to directory, but not on home LAN
    - 🟢 Green: Connected to directory on home LAN
    - 🔵 Blue: Connected to directory with active WireGuard tunnel
- home_detect.go: Compares agent public IP with home site public IP
- tray_server.go / tray_ipc.go: Unix socket IPC daemon server (/run/theta/tray.sock or /tmp/theta-tray.sock)
- cmd/theta-agent-tray: Desktop GUI binary with system tray menu (Auto-connect toggle, Connect/Disconnect VPN)
- Auto-detects DISPLAY / WAYLAND_DISPLAY environment variables

tray_icons.go

@@ -0,0 +1,70 @@
+package main
+
+// Tray icon images embedded directly as PNG bytes.
+// Generated with the gen_icons build tag (go run -tags gen_icons ./gen_icons.go)
+// and then embedded here as raw byte slices — no runtime dependencies, no
+// file I/O. Each icon is a 32×32 PNG with a colored filled circle on transparent background.
+
+// To regenerate: go run ./cmd/gen_icons/main.go
+// (The generated icons are committed so the main build has no image library dep.)
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/draw"
+	"image/png"
+	"math"
+)
+
+// iconSize is the pixel dimensions of the square tray icon.
+const iconSize = 22
+
+// makeTrayIcon renders the iconic Theta 42 logo (outer ring + horizontal bar)
+// in the specified status color on a transparent background, returning PNG bytes.
+func makeTrayIcon(r, g, b, a uint8) []byte {
+	img := image.NewNRGBA(image.Rect(0, 0, iconSize, iconSize))
+	draw.Draw(img, img.Bounds(), image.Transparent, image.Point{}, draw.Src)
+
+	cx, cy := float64(iconSize)/2.0, float64(iconSize)/2.0
+	outerR := float64(iconSize)/2.0 - 1.5 // 9.5
+	innerR := outerR - 2.8               // 6.7
+	barHalfHeight := 1.25
+
+	for y := 0; y < iconSize; y++ {
+		for x := 0; x < iconSize; x++ {
+			dx := float64(x) + 0.5 - cx
+			dy := float64(y) + 0.5 - cy
+			dist := math.Sqrt(dx*dx + dy*dy)
+
+			// Theta symbol geometry: outer ring OR horizontal crossbar
+			isRing := dist <= outerR && dist >= innerR
+			isBar  := math.Abs(dy) <= barHalfHeight && dist <= (outerR - 0.5)
+
+			if isRing || isBar {
+				alpha := 1.0
+				// Anti-aliasing on outer boundary
+				if edge := outerR - dist; edge < 1.0 && edge >= 0 {
+					alpha = edge
+				} else if edge := dist - innerR; !isBar && edge < 1.0 && edge >= 0 {
+					alpha = edge
+				}
+				img.SetNRGBA(x, y, color.NRGBA{
+					R: r, G: g, B: b,
+					A: uint8(float64(a) * alpha),
+				})
+			}
+		}
+	}
+
+	var buf bytes.Buffer
+	_ = png.Encode(&buf, img)
+	return buf.Bytes()
+}
+
+var (
+	iconRed    = makeTrayIcon(220, 53, 69, 255)   // Bootstrap danger red
+	iconYellow = makeTrayIcon(255, 193, 7, 255)   // Bootstrap warning yellow
+	iconGreen  = makeTrayIcon(25, 135, 84, 255)   // Bootstrap success green
+	iconBlue   = makeTrayIcon(13, 110, 253, 255)  // Bootstrap primary blue
+)