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 <[email protected]>

.taskfiles/desktop.yml

@@ -0,0 +1,105 @@
+version: '3'
+
+vars:
+  JLINK_MODULES: "java.base,java.compiler,java.desktop,java.instrument,java.logging,java.management,java.naming,java.net.http,java.prefs,java.rmi,java.scripting,java.security.jgss,java.security.sasl,java.sql,java.transaction.xa,java.xml,java.xml.crypto,jdk.crypto.ec,jdk.crypto.cryptoki,jdk.unsupported"
+
+tasks:
+  prepare:
+    desc: "Prepare desktop build dependencies"
+    deps: [jlink, ":frontend:prepare:desktop", provisioner]
+
+  provisioner:
+    desc: "Build installer provisioner"
+    platforms: [windows]
+    cmds:
+      - node scripts/build-provisioner.mjs
+
+  dev:
+    desc: "Start Tauri desktop dev mode"
+    deps: [prepare]
+    ignore_error: true
+    cmds:
+      - npx tauri dev --no-watch
+
+  build:
+    desc: "Build Tauri desktop app (production)"
+    deps: [prepare]
+    cmds:
+      - npx tauri build
+
+  build:dev:
+    desc: "Build Tauri desktop app (dev, no bundling)"
+    deps: [prepare]
+    cmds:
+      - npx tauri build --no-bundle
+
+  build:dev:mac:
+    desc: "Build Tauri desktop .app bundle (macOS)"
+    deps: [prepare]
+    cmds:
+      - npx tauri build --bundles app
+
+  build:dev:windows:
+    desc: "Build Tauri desktop NSIS installer (Windows)"
+    deps: [prepare]
+    cmds:
+      - npx tauri build --bundles nsis
+
+  build:dev:linux:
+    desc: "Build Tauri desktop AppImage (Linux)"
+    deps: [prepare]
+    cmds:
+      - npx tauri build --bundles appimage
+
+  clean:
+    desc: "Clean Tauri/Cargo build artifacts"
+    cmds:
+      - task: jlink:clean
+      - cd src-tauri && cargo clean
+      - rm -rf dist build
+
+  # ============================================================
+  # JLink — Build bundled Java runtime for Tauri
+  # ============================================================
+
+  jlink:
+    desc: "Build backend JAR and create JLink runtime for Tauri"
+    deps: [jlink:jar, jlink:runtime]
+
+  jlink:jar:
+    desc: "Build backend JAR for Tauri bundling"
+    run: once
+    dir: ..
+    env:
+      DISABLE_ADDITIONAL_FEATURES: "true"
+    cmds:
+      - cmd: cmd /c gradlew.bat bootJar --no-daemon
+        platforms: [windows]
+      - cmd: ./gradlew bootJar --no-daemon
+        platforms: [linux, darwin]
+      - mkdir -p frontend/src-tauri/libs
+      - cp app/core/build/libs/stirling-pdf-*.jar frontend/src-tauri/libs/
+    status:
+      - test -f frontend/src-tauri/libs/stirling-pdf-*.jar
+
+  jlink:runtime:
+    desc: "Create custom JRE with jlink"
+    deps: [jlink:jar]
+    cmds:
+      - rm -rf src-tauri/runtime/jre
+      - mkdir -p src-tauri/runtime
+      - >-
+        jlink
+        --add-modules {{.JLINK_MODULES}}
+        --strip-debug
+        --compress=2
+        --no-header-files
+        --no-man-pages
+        --output src-tauri/runtime/jre
+    status:
+      - test -d src-tauri/runtime/jre
+
+  jlink:clean:
+    desc: "Remove JLink runtime and bundled JARs"
+    cmds:
+      - rm -rf src-tauri/libs src-tauri/runtime