ci(agent): publish the GPU agent image (build-agent job)

Build + push fabledcurator-agent alongside web/ml (own CUDA + onnxruntime-gpu
image, context=agent/, same tag cadence: main → :main/:latest/:c-<sha>, tag →
:<version>). So the operator PULLS + runs it on the GPU machine instead of
building locally. README switched to docker pull.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/README.md

@@ -10,11 +10,11 @@ You run it when you want a burst and stop it to reclaim the card.
 ## 1. Get a token
 In FC: **Settings → Tagging → GPU agent → Generate token** (or Rotate). Copy it.
 
-## 2. Build
+## 2. Pull (CI publishes it alongside the web/ml images)
 ```sh
-cd agent
-docker build -t fc-gpu-agent .
+docker pull git.fabledsword.com/bvandeusen/fabledcurator-agent:latest
 ```
+> Local build for development instead: `docker build -t fc-gpu-agent agent/`
 
 ## 3. Run (on the machine with the GPU)
 ```sh
@@ -22,7 +22,7 @@ docker run --rm --gpus all -p 8770:8770 \
   -e FC_URL=http://curator.traefik.internal \
   -e FC_TOKEN=<paste-the-token> \
   -v fc-agent-models:/models \
-  fc-gpu-agent
+  git.fabledsword.com/bvandeusen/fabledcurator-agent:latest
 ```
 Then open <http://localhost:8770> — the control page. Click **Start** to begin
 draining the queue; **Pause**/**Stop** to yield the GPU. The `-v fc-agent-models`