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/20260116171533_ncmec_submissions.cql

@@ -0,0 +1,10 @@
+CREATE TABLE IF NOT EXISTS fluxer.ncmec_submissions (
+    report_id bigint PRIMARY KEY,
+    status text,
+    ncmec_report_id text,
+    submitted_at timestamp,
+    submitted_by_admin_id bigint,
+    failure_reason text,
+    created_at timestamp,
+    updated_at timestamp
+);