Add Taskfile for unified dev workflow across all components (#6080)

## Add Taskfile for unified dev workflow

### Summary
- Introduces [Taskfile](https://taskfile.dev/) as the single CLI entry
point for all development workflows across backend, frontend, engine,
Docker, and desktop
- ~80 tasks organized into 6 namespaces: `backend:`, `frontend:`,
`engine:`, `docker:`, `desktop:`, plus root-level composites
- All CI workflows migrated to use Task
- Deletes `engine/Makefile` and `scripts/build-tauri-jlink.{sh,bat}` —
replaced by Task equivalents
- Removes redundant npm scripts (`dev`, `build`, `prep`, `lint`, `test`,
`typecheck:all`) from `package.json`
- Smart dependency caching: `sources`/`status`/`generates`
fingerprinting, CI-aware `npm ci` vs `npm install`, `run: once` for
parallel dep deduplication

### What this does NOT do
- Does not replace Gradle, npm, or Docker — Taskfile is a thin
orchestration wrapper
- Does not change application code or behavior

### Install
```
npm install -g @go-task/cli    # or: brew install go-task, winget install Task.Task
```

### Quick start
```
task --list       # discover all tasks
task install      # install all deps
task dev          # start backend + frontend
task dev:all      # also start AI engine
task test         # run all tests
task check        # quick quality gate (local dev)
task check:all    # full CI quality gate
```

### Test plan
- [ ] Install `task` CLI and run `task --list` — verify all tasks
display
- [ ] Run `task install` — verify frontend + engine deps install
- [ ] Run `task dev` — verify backend + frontend start, Ctrl+C exits
cleanly
- [ ] Run `task frontend:check` — verify typecheck + lint + test pass
- [ ] Run `task desktop:dev` — verify jlink builds are cached on second
run
- [ ] Verify CI passes on all workflows

---------

Co-authored-by: James Brunton <jbrunton96@gmail.com>

.taskfiles/backend.yml

@@ -0,0 +1,111 @@
+version: '3'
+
+tasks:
+  dev:
+    desc: "Start backend dev server"
+    ignore_error: true
+    cmds:
+      - cmd: cmd /c gradlew.bat :stirling-pdf:bootRun
+        platforms: [windows]
+      - cmd: ./gradlew :stirling-pdf:bootRun
+        platforms: [linux, darwin]
+
+  build:
+    desc: "Full backend build"
+    cmds:
+      - cmd: cmd /c gradlew.bat clean build
+        platforms: [windows]
+      - cmd: ./gradlew clean build
+        platforms: [linux, darwin]
+
+  build:fast:
+    desc: "Build without tests"
+    cmds:
+      - cmd: cmd /c gradlew.bat clean build -x test
+        platforms: [windows]
+      - cmd: ./gradlew clean build -x test
+        platforms: [linux, darwin]
+
+  build:ci:
+    desc: "Build for CI (formatting checked separately)"
+    cmds:
+      - cmd: cmd /c gradlew.bat build -PnoSpotless
+        platforms: [windows]
+      - cmd: ./gradlew build -PnoSpotless
+        platforms: [linux, darwin]
+
+  test:
+    desc: "Run backend tests"
+    cmds:
+      - cmd: cmd /c gradlew.bat test
+        platforms: [windows]
+      - cmd: ./gradlew test
+        platforms: [linux, darwin]
+
+  format:
+    desc: "Auto-fix code formatting"
+    cmds:
+      - cmd: cmd /c gradlew.bat spotlessApply
+        platforms: [windows]
+      - cmd: ./gradlew spotlessApply
+        platforms: [linux, darwin]
+
+  format:check:
+    desc: "Check code formatting"
+    cmds:
+      - cmd: cmd /c gradlew.bat spotlessCheck
+        platforms: [windows]
+      - cmd: ./gradlew spotlessCheck
+        platforms: [linux, darwin]
+
+  fix:
+    desc: "Auto-fix backend"
+    cmds:
+      - task: format
+
+  swagger:
+    desc: "Generate OpenAPI docs"
+    cmds:
+      - cmd: cmd /c gradlew.bat :stirling-pdf:generateOpenApiDocs
+        platforms: [windows]
+      - cmd: ./gradlew :stirling-pdf:generateOpenApiDocs
+        platforms: [linux, darwin]
+
+  check:
+    desc: "Backend quality gate"
+    cmds:
+      - task: format:check
+      - task: test
+
+  version:
+    desc: "Print project version"
+    silent: true
+    cmds:
+      - cmd: cmd /c gradlew.bat printVersion --quiet | tail -1
+        platforms: [windows]
+      - cmd: ./gradlew printVersion --quiet | tail -1
+        platforms: [linux, darwin]
+
+  licenses:check:
+    desc: "Check dependency licenses"
+    cmds:
+      - cmd: cmd /c gradlew.bat checkLicense --no-parallel
+        platforms: [windows]
+      - cmd: ./gradlew checkLicense --no-parallel
+        platforms: [linux, darwin]
+
+  licenses:generate:
+    desc: "Check and generate dependency license report"
+    cmds:
+      - cmd: cmd /c gradlew.bat checkLicense generateLicenseReport --no-parallel
+        platforms: [windows]
+      - cmd: ./gradlew checkLicense generateLicenseReport --no-parallel
+        platforms: [linux, darwin]
+
+  clean:
+    desc: "Clean build artifacts"
+    cmds:
+      - cmd: cmd /c gradlew.bat clean
+        platforms: [windows]
+      - cmd: ./gradlew clean
+        platforms: [linux, darwin]