Add make check target and CI workflow (#42)

Adds a `make check` target that verifies formatting (gofmt), linting (golangci-lint), and tests (go test -race) without modifying files.

Also adds `.gitea/workflows/check.yml` CI workflow that runs on pushes and PRs to main.

`make check` passes cleanly on current main.

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Co-authored-by: clawbot <clawbot@sneak.berlin>
Reviewed-on: #42
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
Co-committed-by: clawbot <sneak+clawbot@sneak.cloud>

Dockerfile

@@ -0,0 +1,61 @@
+# Lint stage
+# golangci/golangci-lint:v2.11.3-alpine, 2026-03-17
+FROM golangci/golangci-lint:v2.11.3-alpine@sha256:b1c3de5862ad0a95b4e45a993b0f00415835d687e4f12c845c7493b86c13414e AS lint
+
+RUN apk add --no-cache make build-base
+
+WORKDIR /src
+
+# Copy go mod files first for better layer caching
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source code
+COPY . .
+
+# Run formatting check and linter
+RUN make fmt-check
+RUN make lint
+
+# Build stage
+# golang:1.26.1-alpine, 2026-03-17
+FROM golang:1.26.1-alpine@sha256:2389ebfa5b7f43eeafbd6be0c3700cc46690ef842ad962f6c5bd6be49ed82039 AS builder
+
+# Depend on lint stage passing
+COPY --from=lint /src/go.sum /dev/null
+
+ARG VERSION=dev
+
+# Install build dependencies for CGO (mattn/go-sqlite3) and sqlite3 CLI (tests)
+RUN apk add --no-cache make build-base sqlite
+
+WORKDIR /src
+
+# Copy go mod files first for better layer caching
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source code
+COPY . .
+
+# Run tests
+RUN make test
+
+# Build with CGO enabled (required for mattn/go-sqlite3)
+RUN CGO_ENABLED=1 go build -ldflags "-X 'git.eeqj.de/sneak/vaultik/internal/globals.Version=${VERSION}' -X 'git.eeqj.de/sneak/vaultik/internal/globals.Commit=$(git rev-parse HEAD 2>/dev/null || echo unknown)'" -o /vaultik ./cmd/vaultik
+
+# Runtime stage
+# alpine:3.21, 2026-02-25
+FROM alpine:3.21@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709
+
+RUN apk add --no-cache ca-certificates sqlite
+
+# Copy binary from builder
+COPY --from=builder /vaultik /usr/local/bin/vaultik
+
+# Create non-root user
+RUN adduser -D -H -s /sbin/nologin vaultik
+
+USER vaultik
+
+ENTRYPOINT ["/usr/local/bin/vaultik"]