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]>

.github/workflows/ai-engine.yml

@@ -11,10 +11,6 @@ jobs:
     permissions:
       contents: read
       pull-requests: write
-    defaults:
-      run:
-        working-directory: engine
-
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -24,12 +20,12 @@ jobs:
         with:
           enable-cache: true
 
-      - name: Install dependencies
-        run: make install
+      - name: Install Task
+        uses: go-task/setup-task@3be4020d41929789a01026e0e427a4321ce0ad44 # v2.0.0
 
       - name: Run fixers
         # Ignore errors here because we're going to add comments for them in the following steps before actually failing
-        run: make fix || true
+        run: task engine:fix || true
 
       - name: Check for fixer changes
         id: fixer_changes
@@ -60,7 +56,7 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               issue_number: context.issue.number,
-              body: "The Python code in your PR has formatting/linting issues. Consider running `make fix` locally or setting up your editor's Ruff integration to auto-format and lint your files as you go, or commit the suggested changes on this PR.",
+              body: "The Python code in your PR has formatting/linting issues. Consider running `task engine:fix` locally or setting up your editor's Ruff integration to auto-format and lint your files as you go, or commit the suggested changes on this PR.",
             });
 
       - name: Verify fixer changes are committed
@@ -68,16 +64,16 @@ jobs:
         run: |
           if ! git diff --exit-code; then
             echo "Fixes are out of date."
-            echo "Apply the reviewdog suggestions or run 'make fix' from engine/ and commit the updated files."
+            echo "Apply the reviewdog suggestions or run 'task engine:fix' from the repo root and commit the updated files."
             git --no-pager diff --stat
             exit 1
           fi
 
       - name: Run linting
-        run: make lint
+        run: task engine:lint
 
       - name: Run type checking
-        run: make typecheck
+        run: task engine:typecheck
 
       - name: Run tests
-        run: make test
+        run: task engine:test