feat(installation): support asset download via GITHUB_MIRROR_DOMAIN

[wu21-web]

Description

Chinese users without proxies configured can't download assets fast because of network restriction. Adds a GITHUB_MIRROR_DOMAIN check and download assets from it when it is not empty or space.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (describe below)
  Tested on aliyun cloud shell:

shell@Alicloud:~$ wget "https://gh-proxy.com/raw.githubusercontent.com/wu21-web/open-code-review/refs/heads/mirror/install.sh" -O install.sh
--2026-08-13 14:18:00--  https://gh-proxy.com/raw.githubusercontent.com/wu21-web/open-code-review/refs/heads/mirror/install.sh
Resolving gh-proxy.com (gh-proxy.com)... 104.18.42.163, 172.64.147.104, 104.18.42.54, ...
Connecting to gh-proxy.com (gh-proxy.com)|104.18.42.163|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/plain]
Saving to: ‘install.sh’

install.sh                                               [ <=>                                                                                                                 ]   4.03K  --.-KB/s    in 0s      

2026-08-13 14:18:02 (28.3 MB/s) - ‘install.sh’ saved [4122]

shell@Alicloud:~$ openssl dgst -sha256 install.sh 
SHA256(install.sh)= c1309cbfe422b47245bda5e963206a6bffc36d97935c5bf81d5b5a625a863dd9
shell@Alicloud:~$ export GITHUB_MIRROR_DOMAIN='github.dpik.top'
shell@Alicloud:~$ time sh install.sh 
WARNING: Using an unofficial mirror domain, which may lead to SHA256 checksum mismatches and security risks.
downloading ocr v1.9.2 (linux/amd64)...
installed ocr v1.9.2 -> /usr/local/bin/ocr

real    1m16.726s
user    0m0.493s
sys     0m0.219s
shell@Alicloud:~$ echo 'In constrast: '
In constrast: 
shell@Alicloud:~$ time curl -fsSL https://raw.githubusercontent.com/alibaba/open-code-review/main/install.sh | sh
downloading ocr v1.9.2 (linux/amd64)...
curl: (56) Unexpected EOF
error: download failed: https://github.com/alibaba/open-code-review/releases/download/v1.9.2/opencodereview-linux-amd64

real    1m33.425s
user    0m0.074s
sys     0m0.028s

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

[github-actions]

🔍 OpenCodeReview found 2 issue(s) in this PR.

• ✅ Successfully posted inline: 2 comment(s)

[wu21-web]

May I request a review from @stay-foolish-forever ?