feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/fluxer_desktop/build_resources/icons-stable/AppIcon.icon/icon.json

@@ -0,0 +1,28 @@
+{
+	"fill": {
+		"solid": "display-p3:0.27100,0.25562,0.81934,1.00000"
+	},
+	"groups": [
+		{
+			"layers": [
+				{
+					"fill": "automatic",
+					"image-name": "Vector.svg",
+					"name": "Vector"
+				}
+			],
+			"shadow": {
+				"kind": "neutral",
+				"opacity": 0.5
+			},
+			"translucency": {
+				"enabled": true,
+				"value": 0.5
+			}
+		}
+	],
+	"supported-platforms": {
+		"circles": ["watchOS"],
+		"squares": "shared"
+	}
+}