feat(ci): enhance caching strategy and update workflows for pnpm and Go

- Updated CI workflows to export cache paths for pnpm and Go, improving cache efficiency and reducing package download times.
- Replaced corepack enable step with cache path exports in multiple workflows.
- Adjusted cache paths to utilize environment variables for better flexibility and clarity.
- Enhanced README documentation to reflect changes in caching mechanisms and runner configurations.

scripts/ci/pnpm-ci.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env sh
+# pnpm install из кэша Gitea (store + node_modules). Без повторного download при hit.
+set -eu
+: "${PNPM_STORE_DIR:?PNPM_STORE_DIR required — run scripts/ci/export-cache-env.sh first}"
+
+export COREPACK_HOME="${COREPACK_HOME:-${HOME:-/root}/.cache/node/corepack}"
+mkdir -p "$PNPM_STORE_DIR" "$COREPACK_HOME"
+corepack enable
+pnpm config set store-dir "$PNPM_STORE_DIR"
+
+echo "pnpm store: $(pnpm store path)"
+echo "PNPM_CACHE_HIT=${PNPM_CACHE_HIT:-}"
+
+if [ "${PNPM_CACHE_HIT:-}" = "true" ]; then
+  if pnpm install --frozen-lockfile --offline; then
+    echo "pnpm install --offline (cache hit)"
+    exit 0
+  fi
+  echo "offline install failed — prefer-offline"
+fi
+pnpm install --frozen-lockfile --prefer-offline