fix(ci): Switch from buildx to plugins/docker for Harbor auth

The woodpeckerci/plugin-docker-buildx plugin was failing with
"insufficient_scope: authorization failed" when pushing to Harbor,
even though the same credentials worked locally.

Switched to the standard plugins/docker which uses traditional
docker login authentication that may work better with Harbor.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.woodpecker.yml

@@ -85,14 +85,12 @@ steps:
   # Requires secrets: harbor_username, harbor_password
 
   docker-build-api:
-    image: woodpeckerci/plugin-docker-buildx
+    image: plugins/docker
     settings:
       registry: reg.mosaicstack.dev
-      repo: mosaic/api
+      repo: reg.mosaicstack.dev/mosaic/api
       dockerfile: apps/api/Dockerfile
       context: .
-      platforms:
-        - linux/amd64
       tags:
         - "${CI_COMMIT_SHA:0:8}"
         - latest
@@ -100,7 +98,6 @@ steps:
         from_secret: harbor_username
       password:
         from_secret: harbor_password
-      debug: true
     when:
       - branch: [main, develop]
         event: [push, manual]
@@ -108,14 +105,12 @@ steps:
       - build
 
   docker-build-web:
-    image: woodpeckerci/plugin-docker-buildx
+    image: plugins/docker
     settings:
       registry: reg.mosaicstack.dev
-      repo: mosaic/web
+      repo: reg.mosaicstack.dev/mosaic/web
       dockerfile: apps/web/Dockerfile
       context: .
-      platforms:
-        - linux/amd64
       build_args:
         - NEXT_PUBLIC_API_URL=https://api.mosaicstack.dev
       tags:
@@ -125,7 +120,6 @@ steps:
         from_secret: harbor_username
       password:
         from_secret: harbor_password
-      debug: true
     when:
       - branch: [main, develop]
         event: [push, manual]
@@ -133,14 +127,12 @@ steps:
       - build
 
   docker-build-postgres:
-    image: woodpeckerci/plugin-docker-buildx
+    image: plugins/docker
     settings:
       registry: reg.mosaicstack.dev
-      repo: mosaic/postgres
+      repo: reg.mosaicstack.dev/mosaic/postgres
       dockerfile: docker/postgres/Dockerfile
       context: docker/postgres
-      platforms:
-        - linux/amd64
       tags:
         - "${CI_COMMIT_SHA:0:8}"
         - latest
@@ -148,7 +140,6 @@ steps:
         from_secret: harbor_username
       password:
         from_secret: harbor_password
-      debug: true
     when:
       - branch: [main, develop]
         event: [push, manual]