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_app/crates/libfluxcore/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "libfluxcore"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+gif = "0.13"
+image = { version = "0.25.9", default-features = false, features = ["jpeg", "png", "webp", "avif"] }
+png = "0.17"
+ruzstd = { version = "0.7", default-features = false, features = ["std"] }
+wasm-bindgen = { version = "0.2", features = ["std"] }
+serde = { version = "1.0", features = ["derive"] }