ci: rebuild fork image on main source pushes, not just build-definition edits

The merge of the /v1/videos/sync routes produced no image because the
push trigger only watched the workflow file and Containerfile. Now any
Go/UI/deps change on main rebuilds; docs/config-example edits still
don't. (The video-routes image itself was built via manual dispatch,
tag prefix v231.)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AXQxVhXBw8PwFAtsVrXSmj

.gitea/workflows/build-cuda-image.yml

@@ -17,12 +17,19 @@ on:
         description: "llama.cpp CUDA server build (base image tag suffix)"
         required: false
         default: "b9821"
-  # Building the build definition itself kicks off a fresh image.
+  # Any change that lands in the shipped binary or image kicks off a fresh
+  # build (source, UI, deps, build definition). Docs/config-example edits
+  # don't.
   push:
     branches: [main]
     paths:
       - ".gitea/workflows/build-cuda-image.yml"
       - "docker/fork-cuda.Containerfile"
+      - "**/*.go"
+      - "go.mod"
+      - "go.sum"
+      - "ui-svelte/**"
+      - "llama-swap.go"
 
 env:
   REGISTRY: gitea.stevedudenhoeffer.com