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/promote-canary-to-main.yaml

@@ -0,0 +1,67 @@
+name: promote canary -> main
+
+on:
+  workflow_dispatch:
+    inputs:
+      dry_run:
+        type: boolean
+        default: false
+        description: "Show what would change, but don't push"
+      src:
+        type: string
+        default: canary
+        description: 'Source branch'
+      dst:
+        type: string
+        default: main
+        description: 'Destination branch'
+
+concurrency:
+  group: promote-${{ inputs.dst }}
+  cancel-in-progress: false
+
+permissions:
+  contents: read
+
+jobs:
+  promote:
+    runs-on: blacksmith-8vcpu-ubuntu-2404
+    timeout-minutes: 25
+
+    steps:
+      - name: Create GitHub App token
+        id: app-token
+        uses: actions/create-github-app-token@v2
+        with:
+          app-id: ${{ secrets.PROMOTE_APP_ID }}
+          private-key: ${{ secrets.PROMOTE_APP_PRIVATE_KEY }}
+
+      - name: Checkout source
+        uses: actions/checkout@v6
+        with:
+          ref: ${{ inputs.src }}
+          fetch-depth: 0
+          token: ${{ steps.app-token.outputs.token }}
+
+      - name: Verify ff-only + summarize
+        id: verify
+        run: >-
+          python3 scripts/ci/workflows/promote_canary_to_main.py
+          --step verify
+          --src "${{ inputs.src }}"
+          --dst "${{ inputs.dst }}"
+
+      - name: Push fast-forward
+        if: ${{ steps.verify.outputs.ahead != '0' && inputs.dry_run != true }}
+        run: >-
+          python3 scripts/ci/workflows/promote_canary_to_main.py
+          --step push
+          --dst "${{ inputs.dst }}"
+
+      - name: Dry run / no-op
+        if: ${{ steps.verify.outputs.ahead == '0' || inputs.dry_run == true }}
+        run: >-
+          python3 scripts/ci/workflows/promote_canary_to_main.py
+          --step dry_run
+          --dry-run "${{ inputs.dry_run }}"
+          --ahead "${{ steps.verify.outputs.ahead }}"