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/20260113011925_csam_evidence_hold.cql

@@ -0,0 +1,28 @@
+CREATE TABLE IF NOT EXISTS fluxer.csam_evidence_packages (
+    report_id bigint PRIMARY KEY,
+    resource_type text,
+    bucket text,
+    key text,
+    cdn_url text,
+    filename text,
+    content_type text,
+    channel_id bigint,
+    message_id bigint,
+    guild_id bigint,
+    user_id bigint,
+    match_tracking_id text,
+    match_details text,
+    frames text,
+    hashes text,
+    context_snapshot text,
+    created_at timestamp,
+    expires_at timestamp,
+    integrity_sha256 text,
+    evidence_zip_key text
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.csam_evidence_legal_holds (
+    report_id bigint PRIMARY KEY,
+    held_until timestamp,
+    created_at timestamp
+);