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/20260208165214_donation_system_unified.cql

@@ -0,0 +1,46 @@
+CREATE TABLE IF NOT EXISTS fluxer.donors (
+    email text,
+    stripe_customer_id text,
+
+    business_name text,
+    tax_id text,
+    tax_id_type text,
+
+    stripe_subscription_id text,
+    subscription_amount_cents int,
+    subscription_currency text,
+    subscription_interval text,
+    subscription_current_period_end timestamp,
+    subscription_cancel_at timestamp,
+
+    created_at timestamp,
+    updated_at timestamp,
+    version int,
+    PRIMARY KEY ((email))
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.donors_by_stripe_customer_id (
+    stripe_customer_id text,
+    email text,
+    PRIMARY KEY ((stripe_customer_id), email)
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.donors_by_stripe_subscription_id (
+    stripe_subscription_id text,
+    email text,
+    PRIMARY KEY ((stripe_subscription_id), email)
+);
+
+CREATE TABLE IF NOT EXISTS fluxer.donor_magic_link_tokens (
+    token_ text,
+    donor_email text,
+    expires_at timestamp,
+    used_at timestamp,
+    PRIMARY KEY ((token_))
+) WITH default_time_to_live = 900;
+
+CREATE TABLE IF NOT EXISTS fluxer.donor_magic_link_tokens_by_email (
+    donor_email text,
+    token_ text,
+    PRIMARY KEY ((donor_email), token_)
+) WITH default_time_to_live = 900;