feat(infra): full Nix migration — all 6 services + CI/CD

- flake.nix: 6 derivations (hub, scraper, tools-gateway, tools-workers, tools-frontend, llm-api)
- Fetch submodule source via builtins.fetchGit with pinned revs
- Fix cargo HOME/TMPDIR for Nix sandbox permission issues
- Fix llm-api: CMake/Clang deps for llama.cpp-sys2 bindgen
- Add LIBCLANG_PATH, LD_LIBRARY_PATH for Rust bindgen builds
- Systemd units: tools-gateway (3501), tools-frontend (3500), tools-workers, llm-api (8080)
- tools.target for grouped management
- Env configs: /etc/tools/env, /etc/llm-api/env
- GitHub Actions: nix-build.yml — matrix build + nix copy + deploy
- Update Traefik apps.yaml: tools/host.docker.internal:3500, llm-api/host.docker.internal:8080
- iptables: allow Docker→host on 3099, 4091, 3500, 3501, 8080
- Add scripts/nix-deploy.sh for CI/CD deploy step

scripts/nix-deploy.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# ── Nix Deploy — VPS-side script ──
+# Runs after `nix copy --to ssh://VPS ./result` from CI
+# Usage: sudo ./deploy.sh <service-name>
+set -euo pipefail
+
+SERVICE="$1"
+PROFILE="/nix/var/nix/profiles/${SERVICE}"
+
+# Find the latest store path for this service
+LATEST=$(ls -1d /nix/store/*-"${SERVICE}"-* 2>/dev/null | tail -1)
+if [ -z "$LATEST" ]; then
+  echo "ERROR: No store path found for ${SERVICE}"
+  exit 1
+fi
+
+# Update profile
+/nix/var/nix/profiles/default/bin/nix-env --profile "$PROFILE" --set "$LATEST"
+
+# Restart service
+systemctl daemon-reload
+systemctl enable --now "${SERVICE}" 2>/dev/null || systemctl restart "${SERVICE}"
+
+echo "Deployed ${SERVICE}: ${LATEST}"
+systemctl is-active "${SERVICE}"
+
+# Collect garbage (safe: only removes unreachable paths)
+# nix-collect-garbage -d 2>/dev/null || true