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/.github/workflows/test-cassandra-backup.yaml

@@ -0,0 +1,90 @@
+name: test cassandra-backup
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 */2 * * *'
+
+concurrency:
+  group: test-cassandra-backup
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  test-backup:
+    name: Test latest Cassandra backup
+    runs-on: blacksmith-8vcpu-ubuntu-2404
+    timeout-minutes: 45
+
+    env:
+      CASSANDRA_IMAGE: cassandra:5.0.6
+      CASS_CONTAINER: cass-${{ github.run_id }}-${{ github.run_attempt }}
+      UTIL_CONTAINER: cass-util-${{ github.run_id }}-${{ github.run_attempt }}
+      CASS_VOLUME: cassandra-data-${{ github.run_id }}-${{ github.run_attempt }}
+      BACKUP_VOLUME: cassandra-backup-${{ github.run_id }}-${{ github.run_attempt }}
+      MAX_HEAP_SIZE: 2G
+      HEAP_NEWSIZE: 512M
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Set temp paths
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step set_temp_paths
+
+      - name: Pre-clean
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step pre_clean
+
+      - name: Install tools
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step install_tools
+
+      - name: Find latest backup, validate freshness, download, decrypt, extract into Docker volume
+        env:
+          B2_KEY_ID: ${{ secrets.B2_KEY_ID }}
+          B2_APPLICATION_KEY: ${{ secrets.B2_APPLICATION_KEY }}
+          AGE_PRIVATE_KEY: ${{ secrets.CASSANDRA_AGE_PRIVATE_KEY }}
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step fetch_backup
+
+      - name: Create data volume
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step create_data_volume
+
+      - name: Restore keyspaces into volume and promote snapshot SSTables
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step restore_keyspaces
+
+      - name: Start Cassandra
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step start_cassandra
+
+      - name: Verify data
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step verify_data
+
+      - name: Cleanup
+        if: always()
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step cleanup
+
+      - name: Report status
+        if: always()
+        env:
+          JOB_STATUS: ${{ job.status }}
+        run: >-
+          python3 scripts/ci/workflows/test_cassandra_backup.py
+          --step report_status