[BUG] examples/gateway/gcp/setup.sh: CLAUDE_SHA256 pin compared case-sensitively - uppercase pins (PowerShell Get-FileHash) fail the build

**Note:** This is a bug in the repo's example deployment assets (`examples/gateway/gcp/setup.sh`), not in the Claude Code CLI itself — so the CLI bug-form fields (version/model/terminal) don't apply. I have a tested 2-line fix ready, but external PR creation appears to be disabled on this repo (no non-maintainer PR since 2026-08-16; `createPullRequest` is rejected via both GraphQL and REST), so I'm filing the report here instead.

## What's wrong?

`examples/gateway/gcp/setup.sh` accepts an optional out-of-band checksum pin, `CLAUDE_SHA256`, and compares it against `openssl dgst` output **case-sensitively**:

```bash
if [[ -n "${CLAUDE_SHA256}" && "$(sha_of "${CLAUDE_BINARY}")" != "${CLAUDE_SHA256}" ]]; then
echo "ERROR: sha256 of ${CLAUDE_BINARY} does not match CLAUDE_SHA256 (${CLAUDE_SHA256}) — refusing to build." >&2
exit 1
fi
```

`openssl` always emits lowercase hex, but some common tools publish checksums in uppercase — e.g. PowerShell's `Get-FileHash`. An operator who pins the **correct** checksum in uppercase gets a spurious "refusing to build" failure on a binary that actually verifies. The error message is misleading, because the hashes are equal apart from case.

The AWS sibling script already guards against exactly this — `examples/gateway/aws/setup.sh` normalizes its equivalent pin:

```bash
DIST_SHA256="${DIST_SHA256,,}" # normalize to lowercase — openssl emits lowercase hex; some tools (PowerShell Get-FileHash) publish uppercase
```

The GCP script has no such normalization, so the two examples silently disagree on whether an uppercase pin works.

## What should happen?

A correct checksum pin should verify regardless of hex case, matching the AWS example's documented behavior.

## Steps to reproduce

1. `cd examples/gateway/gcp`
2. Compute the correct sha256 of a `./claude` binary in uppercase (as `Get-FileHash` reports it): `CLAUDE_SHA256="$(openssl dgst -sha256 ./claude | awk '{print toupper($NF)}')"`
3. Run `./setup.sh` far enough to reach the image build step.
4. The script exits with `ERROR: sha256 of ./claude does not match CLAUDE_SHA256 (...) — refusing to build.` even though the checksum is correct.

## Fix (2 lines, tested)

Normalize the pin where it is read, mirroring the AWS script's comment — but using `tr` rather than the bash-4-only `${VAR,,}` expansion, which is itself broken on stock macOS bash 3.2 (see #82320, which converts the AWS script to this same portable idiom):

```diff
CLAUDE_SHA256="${CLAUDE_SHA256:-}" # optional: out-of-band sha256 pin for the downloaded binary, checked in addition to the release manifest
+# normalize to lowercase — openssl emits lowercase hex; some tools (PowerShell Get-FileHash) publish uppercase
+CLAUDE_SHA256="$(printf '%s' "${CLAUDE_SHA256}" | LC_ALL=C tr '[:upper:]' '[:lower:]')"
```

An empty value stays empty, so the "pin is optional" gate (`[[ -n "${CLAUDE_SHA256}" ... ]]`) is unchanged. Verified with `bash -n` and a functional check (uppercase pin normalizes and matches; empty pin still skips the check).

The commit is ready on a fork branch if PRs are re-enabled: https://github.com/Rikinshah787/claude-code/tree/fix-gcp-claude-sha256-case ([compare view](https://github.com/anthropics/claude-code/compare/main...Rikinshah787:claude-code:fix-gcp-claude-sha256-case)).

Read examples/gateway/gcp/setup.sh at the CLAUDE_SHA256 assignment and checksum comparison, then compare the normalization already used in examples/gateway/aws/setup.sh. Run bash -n and the functional checks described in the issue; done means uppercase pins verify successfully while an empty optional pin still skips the check.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.