ci: build image on dashboard static changes too

api/static/** ships inside the image but wasn't in the docker workflow's
paths filter — dashboard-only commits (a6da02f trigger-row reasoning,
81bf154, da17be8) silently produced no image and only reached production
by riding along with later .py commits.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/docker.yml

@@ -9,6 +9,7 @@ on:
       - "Dockerfile"
       - "requirements.txt"
       - "**.py"
+      - "api/static/**"
       - ".github/workflows/docker.yml"
   workflow_dispatch: