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/20251225183000_reports_dsa.cql

@@ -0,0 +1,20 @@
+ALTER TABLE fluxer.iar_submissions ADD reporter_email text;
+ALTER TABLE fluxer.iar_submissions ADD reporter_full_legal_name text;
+ALTER TABLE fluxer.iar_submissions ADD reporter_country_of_residence text;
+ALTER TABLE fluxer.iar_submissions ADD reported_guild_invite_code text;
+
+CREATE TABLE IF NOT EXISTS fluxer.dsa_report_email_verifications (
+    email_lower text,
+    code_hash text,
+    expires_at timestamp,
+    last_sent_at timestamp,
+    PRIMARY KEY ((email_lower))
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.dsa_report_tickets (
+    ticket text,
+    email_lower text,
+    expires_at timestamp,
+    created_at timestamp,
+    PRIMARY KEY ((ticket))
+);