chore(deps): bump knip 6.14.1 → 6.14.2 and docker/metadata-action v5 → v6

Both are Dependabot bumps that have been waiting on the queue; landing
them directly so the lock files stay coherent with the rest of v1.5.5.

knip: minor; docker/metadata-action: clean major (workflow change is
exactly the @v5 → @v6 string in two places).

Closes #209
Closes #183

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/docker-publish.yml

@@ -101,7 +101,7 @@ jobs:
 
       - name: Compute image labels
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: ${{ env.IMAGE_REF }}
           labels: |
@@ -275,7 +275,7 @@ jobs:
 
       - name: Compute image tags & labels
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: ${{ env.IMAGE_REF }}
           tags: |