Add automatic Docker builds on main branch

- docker-dev: Builds and pushes :dev tag on every main push
- docker-release: Builds :latest and :vX.Y.Z on tags
- docker-verify: Dry-run build on PRs

Updated README with Docker tag documentation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.woodpecker.yml

@@ -60,8 +60,29 @@ steps:
       - event: [push, tag]
         branch: main
 
-  # Build and push Docker image (tags only)
-  package-docker:
+  # Build and push Docker image (main branch - dev tag)
+  docker-dev:
+    image: *docker_image
+    settings:
+      repo: ghcr.io/barryw/paperlessmcp
+      dockerfile: PaperlessMCP/Dockerfile
+      context: PaperlessMCP
+      platforms:
+        - linux/amd64
+        - linux/arm64
+      tag: dev
+      registry: ghcr.io
+      username:
+        from_secret: github_username
+      password:
+        from_secret: github_token
+    depends_on: [version]
+    when:
+      - event: push
+        branch: main
+
+  # Build and push Docker image (tags - release)
+  docker-release:
     image: *docker_image
     settings:
       repo: ghcr.io/barryw/paperlessmcp
@@ -105,6 +126,6 @@ steps:
       files:
         - artifacts/*.nupkg
       title: ${CI_COMMIT_TAG}
-    depends_on: [package-nuget, package-docker]
+    depends_on: [package-nuget, docker-release]
     when:
       - event: tag