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.

.github/workflows/deploy.yml

@@ -1,4 +1,4 @@
-name: Build & Deploy (Nix)
+name: Build & Deploy (Bun)
 
 on:
   push:
@@ -25,26 +25,27 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v22
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
         with:
-          determinate: false
-          extra-conf: |
-            sandbox = false
-            accept-flake-config = true
+          bun-version: 1.3.14
 
-      - name: Cache Nix
-        uses: DeterminateSystems/magic-nix-cache-action@v14
+      - name: Install deps
+        run: bun install --frozen-lockfile
 
-      - name: Build zesdex
-        id: build
+      - name: Type-check
+        run: bun run check
+
+      - name: Test
+        run: bun test
+
+      - name: Build binary
         run: |
-          nix build .#default --impure --option sandbox false --print-build-logs
-          STORE_PATH=$(readlink result)
-          echo "store-path=$STORE_PATH" >> "$GITHUB_OUTPUT"
-          echo "Build OK: $STORE_PATH"
+          bun run build
+          test -x dist/zesdex && echo "binary OK ($(stat -c%s dist/zesdex) bytes)"
 
       - name: Setup SSH key
+        if: env.VPS_HOST != '' && env.VPS_HOST != 'null'
         env:
           SSH_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
         run: |
@@ -56,6 +57,7 @@ jobs:
           ssh-keyscan -H "$VPS_HOST" >> ~/.ssh/known_hosts 2>/dev/null
 
       - name: Deploy zesdex to VPS
+        if: env.VPS_HOST != '' && env.VPS_HOST != 'null'
         run: |
-          STORE_PATH="${{ steps.build.outputs.store-path }}"
-          ssh "$VPS_USER@$VPS_HOST" "nix copy --to file:///nix/store $STORE_PATH && nix-env --install --force $STORE_PATH --profile /nix/var/nix/profiles/zesdex && systemctl restart zesdex"
+          scp dist/zesdex "$VPS_USER@$VPS_HOST:/usr/local/bin/zesdex"
+          ssh "$VPS_USER@$VPS_HOST" "chmod +x /usr/local/bin/zesdex && systemctl restart zesdex"

.github/workflows/flakehub-publish-rolling.yaml

@@ -1,20 +0,0 @@
-name: Publish to FlakeHub
-
-on:
-  push:
-    branches: [main, master]
-  workflow_dispatch:
-
-jobs:
-  flakehub-publish:
-    runs-on: ubuntu-latest
-    permissions:
-      id-token: write
-      contents: read
-    steps:
-      - uses: actions/checkout@v6
-      - uses: DeterminateSystems/determinate-nix-action@main
-      - uses: DeterminateSystems/flakehub-push@main
-        with:
-          visibility: public
-          rolling: true