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/CALL_DELETE.json

@@ -0,0 +1,18 @@
+{
+	"$schema": "https://json-schema.org/draft/2020-12/schema",
+	"name": "CALL_DELETE",
+	"description": "Sent when a DM or group DM call ends.",
+	"scope": "presence",
+	"dispatchedBy": ["gateway"],
+	"note": "Dispatched to all recipients when the call terminates (all participants leave or timeout)",
+	"payload": {
+		"type": "object",
+		"properties": {
+			"channel_id": {
+				"type": "string",
+				"description": "Channel ID of the ended call"
+			}
+		},
+		"required": ["channel_id"]
+	}
+}