fix: add setup-just to CI workflows

Both smoke and nightly workflows use `just` but never installed it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: groksrc

.github/workflows/benchmark-nightly.yml

@@ -13,6 +13,8 @@ jobs:
 
       - uses: astral-sh/setup-uv@v4
 
+      - uses: extractions/setup-just@v2
+
       - name: Install dependencies
         run: uv sync --group dev --extra judge
 

.github/workflows/benchmark-smoke.yml

@@ -12,6 +12,8 @@ jobs:
 
       - uses: astral-sh/setup-uv@v4
 
+      - uses: extractions/setup-just@v2
+
       - name: Install dependencies
         run: uv sync --group dev