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_devops/cassandra/migrations/20251207120000_email_change.cql

@@ -0,0 +1,25 @@
+CREATE TABLE IF NOT EXISTS fluxer.email_change_tickets (
+	ticket text PRIMARY KEY,
+	user_id bigint,
+	require_original boolean,
+	original_email text,
+	original_verified boolean,
+	original_code text,
+	original_code_sent_at timestamp,
+	original_code_expires_at timestamp,
+	new_email text,
+	new_code text,
+	new_code_sent_at timestamp,
+	new_code_expires_at timestamp,
+	status text,
+	created_at timestamp,
+	updated_at timestamp
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.email_change_tokens (
+	token_ text PRIMARY KEY,
+	user_id bigint,
+	new_email text,
+	expires_at timestamp,
+	created_at timestamp
+);