security: harden Docker and release CI workflows

- Pin all GitHub Actions to commit SHA to prevent supply chain attacks
- Enable SLSA provenance attestation (mode=max) and SBOM generation
- Add cosign keyless signing for Docker images via GitHub OIDC
- Capture and output image digests to GitHub Job Summary
- Pin Dockerfile base images to digest (bun:1, golang:1.26.1-alpine, debian:bookworm-slim)
- Add SHA256 checksum generation for binary releases (Linux/macOS/Windows)
- Update actions/checkout v3->v4, actions/setup-go v3->v5 in release.yml

Dockerfile

@@ -1,4 +1,4 @@
-FROM oven/bun:latest AS builder
+FROM oven/bun:1@sha256:0733e50325078969732ebe3b15ce4c4be5082f18c4ac1a0f0ca4839c2e4e42a7 AS builder
 
 WORKDIR /build
 COPY web/package.json .
@@ -8,7 +8,7 @@ COPY ./web .
 COPY ./VERSION .
 RUN DISABLE_ESLINT_PLUGIN='true' VITE_REACT_APP_VERSION=$(cat VERSION) bun run build
 
-FROM golang:alpine AS builder2
+FROM golang:1.26.1-alpine@sha256:2389ebfa5b7f43eeafbd6be0c3700cc46690ef842ad962f6c5bd6be49ed82039 AS builder2
 ENV GO111MODULE=on CGO_ENABLED=0
 
 ARG TARGETOS
@@ -25,7 +25,7 @@ COPY . .
 COPY --from=builder /build/dist ./web/dist
 RUN go build -ldflags "-s -w -X 'github.com/QuantumNous/new-api/common.Version=$(cat VERSION)'" -o new-api
 
-FROM debian:bookworm-slim
+FROM debian:bookworm-slim@sha256:f06537653ac770703bc45b4b113475bd402f451e85223f0f2837acbf89ab020a
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends ca-certificates tzdata libasan8 wget \