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_docs/schemas/events/SESSIONS_REPLACE.json

@@ -0,0 +1,34 @@
+{
+	"$schema": "https://json-schema.org/draft/2020-12/schema",
+	"name": "SESSIONS_REPLACE",
+	"description": "User sessions have been replaced. Sent when sessions are updated across devices.",
+	"scope": "presence",
+	"dispatchedBy": ["gateway"],
+	"payload": {
+		"type": "array",
+		"items": {
+			"type": "object",
+			"properties": {
+				"session_id": {
+					"type": "string",
+					"description": "Session identifier ('all' for aggregated status, or specific session ID)"
+				},
+				"status": {
+					"type": "string",
+					"enum": ["online", "offline", "idle", "dnd", "invisible"],
+					"description": "Current status of the session"
+				},
+				"mobile": {
+					"type": "boolean",
+					"description": "Whether this session is from a mobile device"
+				},
+				"afk": {
+					"type": "boolean",
+					"description": "Whether this session is AFK"
+				}
+			},
+			"required": ["session_id", "status", "mobile", "afk"]
+		},
+		"description": "Array of session status entries. Includes an 'all' entry with aggregated status plus individual session entries."
+	}
+}