Move engine Dockerfiles under docker/ and fix build:engine task (#7869)

# Description of Changes

- `task docker:build:engine` was broken: `dir: engine` made the build
context `engine/`, but `engine/Dockerfile` uses root-relative `COPY
engine/...` paths, so it failed with `"/engine/src": not found`
- Root cause: #7386 switched the Dockerfile to root-relative paths and
updated the CI workflows, but not `.taskfiles/docker.yml`. CI stayed
green, so only local `task` users were affected
- Moved `engine/Dockerfile` and `engine/Dockerfile.dev` to
`docker/engine/`, so all Dockerfiles now live under `docker/` (these two
were the only outliers)
- Updated the 6 references in `ai-engine.yml`, `push-docker.yml`,
`Saas-Dev-Deploy.yml` and `PR-Demo-Comment-with-react.yml`
- Added `docker/engine/**` to the `engine` filter in `.files.yaml` so
engine Dockerfile changes still trigger AI Engine CI
- Added `docker:build:engine:dev`, matching the `Dockerfile.dev` build
CI already runs
- `build:engine` now follows the same `-f <path> .` pattern as its five
sibling build tasks

Dockerfile contents are unchanged (pure renames). Note: with the files
under `docker/`, edits to them now also match the `project`, `frontend`
and `dockerfiles` filters, so they run more CI jobs than before.

### Verified locally

- `task docker:build:engine`, `task docker:build:engine:dev`
- Both CI commands verbatim: `docker build --file
docker/engine/Dockerfile[.dev] --tag ... .`
- `task pre-commit` clean

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] Every comment I added says something the code does not
([guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/CODE_COMMENTS.md))
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have run `task check` to verify linters, typechecks, and tests
pass
- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#7-testing)
for more details.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: Frooodle

.github/config/.files.yaml

@@ -125,6 +125,7 @@ tauri: &tauri
 engine: &engine
   - *ci
   - engine/**
+  - docker/engine/**
   - app/(common|core|proprietary|saas)/src/main/java/**
   - .github/workflows/ai-engine.yml
   - Taskfile.yml

.github/workflows/PR-Demo-Comment-with-react.yml

@@ -254,7 +254,7 @@ jobs:
         uses: docker/build-push-action@53b7df96c91f9c12dcc8a07bcb9ccacbed38856a # v7.3.0
         with:
           context: .
-          file: ./engine/Dockerfile
+          file: ./docker/engine/Dockerfile
           push: true
           cache-from: type=gha,scope=stirling-pdf-engine
           cache-to: type=gha,mode=max,scope=stirling-pdf-engine

.github/workflows/Saas-Dev-Deploy.yml

@@ -101,7 +101,7 @@ jobs:
         uses: docker/build-push-action@53b7df96c91f9c12dcc8a07bcb9ccacbed38856a # v7.3.0
         with:
           context: .
-          file: ./engine/Dockerfile
+          file: ./docker/engine/Dockerfile
           push: true
           cache-from: type=gha,scope=stirling-saas-engine
           cache-to: type=gha,mode=max,scope=stirling-saas-engine

.github/workflows/ai-engine.yml

@@ -100,11 +100,11 @@ jobs:
 
       - name: Build engine production image
         if: always()
-        run: docker build --file engine/Dockerfile --tag stirling-pdf-engine:ci .
+        run: docker build --file docker/engine/Dockerfile --tag stirling-pdf-engine:ci .
 
       - name: Build engine development image
         if: always()
-        run: docker build --file engine/Dockerfile.dev --tag stirling-pdf-engine-dev:ci .
+        run: docker build --file docker/engine/Dockerfile.dev --tag stirling-pdf-engine-dev:ci .
 
       - name: Remove engine check comment on success
         if: steps.engine-check.outcome == 'success' && github.event_name == 'pull_request'

.github/workflows/push-docker.yml

@@ -405,7 +405,7 @@ jobs:
         if: env.RUN_ENGINE == 'true'
         run: |
           set -eu
-          hash=$( { cat engine/Dockerfile engine/pyproject.toml engine/uv.lock engine/.env; \
+          hash=$( { cat docker/engine/Dockerfile engine/pyproject.toml engine/uv.lock engine/.env; \
                     find engine/src -type f -print0 | sort -z | xargs -0 cat; } \
                   | sha256sum | cut -d' ' -f1)
           echo "hash=${hash}" >> "$GITHUB_OUTPUT"
@@ -487,7 +487,7 @@ jobs:
         with:
           builder: ${{ steps.buildx.outputs.name }}
           context: .
-          file: ./engine/Dockerfile
+          file: ./docker/engine/Dockerfile
           push: true
           cache-from: type=gha,scope=stirling-engine
           cache-to: type=gha,mode=max,scope=stirling-engine

.taskfiles/docker.yml

@@ -3,6 +3,7 @@ version: '3'
 vars:
   COMPOSE_DIR: docker/compose
   EMBEDDED_DIR: docker/embedded
+  ENGINE_DIR: docker/engine
 
 tasks:
   build:
@@ -32,9 +33,13 @@ tasks:
 
   build:engine:
     desc: "Build engine Docker image"
-    dir: engine
     cmds:
-      - docker build -t stirling-pdf-engine .
+      - docker build -t stirling-pdf-engine -f {{.ENGINE_DIR}}/Dockerfile .
+
+  build:engine:dev:
+    desc: "Build engine development Docker image"
+    cmds:
+      - docker build -t stirling-pdf-engine-dev -f {{.ENGINE_DIR}}/Dockerfile.dev .
 
   up:
     desc: "Start standard docker compose stack"