chore: hapus infra Nix Rust mati; deploy.yml rombak ke Bun native

Semua flake/default/shell merujuk Cargo.lock + crate 'zesdex-gateway' yang
sudah dihapus saat rombak monorepo ke project tunggal Bun, sehingga
nix build .#default pasti gagal. Hapus infra Nix yang tak bisa dipakai:

- hapus flake.nix, default.nix, shell.nix, flakehub-publish-rolling.yaml
- deploy.yml: ganti nix build .#default -> setup-bun + bun build --compile
  + scp dist/zesdex -> /usr/local/bin/zesdex -> systemctl restart zesdex
- docker-compose.yml: RUST_LOG usang -> ZESDEX_API_PORT (env TS)

verify: tsc 0 err, bun test 79 pass, dist/zesdex build OK.

docker-compose.yml

@@ -12,7 +12,7 @@ services:
       - ./workspace:/workspace:ro
     environment:
       - ZESDEX_DATA_DIR=/data
-      - RUST_LOG=${RUST_LOG:-info}
+      - ZESDEX_API_PORT=${ZESDEX_API_PORT:-8080}
     stdin_open: true
     tty: true
     # For daemon mode, expose the IPC socket directory