fix(ci): use workspace dir for training output (permission denied on /output)

CI runner pods don't have write access to root filesystem.
Use ${CI_PROJECT_DIR}/output instead of /output for training artifacts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitlab-ci.yml

@@ -453,7 +453,7 @@ build-training:
   before_script:
     - export LD_LIBRARY_PATH=$(echo "$LD_LIBRARY_PATH" | tr ':' '\n' | grep -v stubs | tr '\n' ':' | sed 's/:$//')
     - nvidia-smi
-    - mkdir -p /output
+    - mkdir -p ${CI_PROJECT_DIR}/output
 
 train-validate-dqn:
   extends: .train-validate-base
@@ -463,7 +463,7 @@ train-validate-dqn:
         --model dqn
         --symbol ES.FUT
         --data-dir /mnt/training-data/futures-baseline
-        --output-dir /output
+        --output-dir ${CI_PROJECT_DIR}/output
         --max-steps-per-epoch 50
     - echo "DQN validation passed"
 
@@ -475,7 +475,7 @@ train-validate-tft:
         --model tft
         --symbol ES.FUT
         --data-dir /mnt/training-data/futures-baseline
-        --output-dir /output
+        --output-dir ${CI_PROJECT_DIR}/output
         --max-steps-per-epoch 50
     - echo "TFT validation passed"