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/20260217140000_guild_discovery.cql

@@ -0,0 +1,21 @@
+CREATE TABLE IF NOT EXISTS fluxer.guild_discovery (
+    guild_id bigint,
+    status text,
+    category_type int,
+    description text,
+    applied_at timestamp,
+    reviewed_at timestamp,
+    reviewed_by bigint,
+    review_reason text,
+    removed_at timestamp,
+    removed_by bigint,
+    removal_reason text,
+    PRIMARY KEY ((guild_id))
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.guild_discovery_by_status (
+    status text,
+    applied_at timestamp,
+    guild_id bigint,
+    PRIMARY KEY ((status), applied_at, guild_id)
+) WITH CLUSTERING ORDER BY (applied_at DESC, guild_id DESC);