Redesign icon: wood texture shield with darken-blended Syncthing motif

Replace procedural icon renderer with pre-rendered textured icons:
- Use Stammtisch wood texture as shield face (crop tabletop planks)
- Apply Syncthing motif via darken blend ("warpaint on wood" effect)
- Fix Syncthing logo geometry: asymmetric node placement (76°/116°/168°
  gaps) with offset hub, matching the official SVG
- Metal rim with rivets and directional lighting
- Embed pre-rendered PNGs via go:embed (no runtime rendering)
- Icon generator in cmd/icongen/ takes wood texture as input

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

internal/icons/states.go

@@ -1,7 +1,5 @@
 package icons
 
-import "image/color"
-
 // State represents the current sync state for icon rendering.
 type State int
 
@@ -12,19 +10,3 @@ const (
 	StateError                     // Red — folder error
 	StateDisconnected              // Dark gray — cannot reach Syncthing
 )
-
-// colors maps each state to its icon color.
-var colors = map[State]color.RGBA{
-	StateIdle:         {76, 175, 80, 255},   // green
-	StateSyncing:      {33, 150, 243, 255},  // blue
-	StatePaused:       {158, 158, 158, 255}, // gray
-	StateError:        {244, 67, 54, 255},   // red
-	StateDisconnected: {97, 97, 97, 255},    // dark gray
-}
-
-func colorForState(s State) color.RGBA {
-	if c, ok := colors[s]; ok {
-		return c
-	}
-	return colors[StateDisconnected]
-}