CI: add pre-baked ci-base image (producer) [Phase 1a] (#637)

Dockerfile.ci

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+# Pre-baked CI base image for Woodpecker pipelines.
+#
+# Purpose: eliminate the cold `pnpm install` that dominates every pipeline
+# (~731s median). This image ships the native toolchain (no per-run `apk add`)
+# AND a warm, content-addressable pnpm store with the dependency-tree tarballs
+# already fetched at build time. `pnpm fetch` only populates the store from the
+# lockfile — it does NOT run the native node-gyp builds (better-sqlite3,
+# node-pty, sqlite3, canvas, sharp); those still compile at `pnpm install`,
+# which is exactly why the musl toolchain stays baked into this image. A
+# pipeline `pnpm install --frozen-lockfile --prefer-offline` then resolves
+# tarballs from local hard-links (no network) and compiles natives against the
+# already-present toolchain, in tens of seconds instead of ~731s.
+#
+# Rebuilt only when `pnpm-lock.yaml` or this Dockerfile change
+# (see .woodpecker/ci-image.yml).
+#
+# Node version is intentionally pinned to 22 (Active LTS at time of writing).
+# The node:22 -> node:24 bump lands as a SEPARATE follow-up PR so the cache
+# change carries zero runtime-version variables.
+FROM node:22-alpine
+
+# Native toolchain required to compile node-gyp deps on musl, plus the
+# postgresql-client used by the test step's pg_isready readiness probe. `bash`
+# is baked here too — the sanitization step in ci.yml otherwise does a per-run
+# `apk add bash`.
+RUN apk add --no-cache python3 make g++ postgresql-client bash
+
+# Pin pnpm to the repo's packageManager version via corepack.
+RUN corepack enable && corepack prepare pnpm@10.6.2 --activate
+
+WORKDIR /app
+
+# Pin the store location so the pipeline can point `store-dir` at the same path.
+ENV PNPM_HOME=/root/.local/share/pnpm
+RUN pnpm config set store-dir /root/.local/share/pnpm/store
+
+# Warm the store. `pnpm fetch` populates the content-addressable store with the
+# dependency tarballs directly from the lockfile (no package.json / workspace
+# needed), so a baked store stays valid until the lockfile changes. Note:
+# `fetch` does NOT compile native modules — that happens later at `pnpm install`
+# in the pipeline, against the toolchain baked above.
+COPY pnpm-lock.yaml ./
+RUN pnpm fetch --frozen-lockfile