chore: add Taskfile with the check quality gate

Defines `task check` (fmt-check + vet + lint + test) — the gate ADR-009 and CI
both invoke. Also `task skills` to wire the engineering skills library via the
canonical installer (symlinks, gitignored). lint no-ops locally when
golangci-lint is absent; CI installs it.

Taskfile.yml

@@ -0,0 +1,52 @@
+version: "3"
+
+# Quality gate for Tapir. `task check` is THE gate referenced by ADR-009 and the
+# CI workflow. Run it before every push (TBD: commit directly to main).
+
+tasks:
+  default:
+    cmds:
+      - task: check
+
+  check:
+    desc: Full quality gate — fmt check, vet, lint, test.
+    cmds:
+      - task: fmt-check
+      - task: vet
+      - task: lint
+      - task: test
+
+  fmt:
+    desc: Format all Go code.
+    cmds:
+      - gofmt -w .
+
+  fmt-check:
+    desc: Fail if any file is not gofmt-clean.
+    cmds:
+      - test -z "$(gofmt -l .)" || { echo 'gofmt: files need formatting:'; gofmt -l .; exit 1; }
+
+  vet:
+    desc: go vet.
+    cmds:
+      - go vet ./...
+
+  lint:
+    desc: golangci-lint (installed by CI; skipped locally if absent).
+    cmds:
+      - 'command -v golangci-lint >/dev/null 2>&1 && golangci-lint run ./... || echo "golangci-lint not installed — skipping (CI installs it)"'
+
+  test:
+    desc: Run all tests, including the acceptance suite (RED until the engine is implemented).
+    cmds:
+      - go test ./...
+
+  build:
+    desc: Compile the binary.
+    cmds:
+      - go build -o bin/tapir ./cmd/tapir
+
+  skills:
+    desc: Wire the engineering skills library into this repo (symlinks, gitignored).
+    cmds:
+      - curl -fsSL https://gitea.d-ma.be/mathias/skills/raw/branch/main/install.sh | bash