Changes

feat(pipelines/tiflash): migrate fileserver.pingcap.net artifacts to OCI registry (#4268)

Removes all `fileserver.pingcap.net` references from `pingcap/tiflash`
Jenkins pipelines across all active branches, replacing with OCI-based
artifact access.

## Changes

- **Remove `FILE_SERVER_URL` env var** — was defined in 31 pipeline
files but never referenced via `$FILE_SERVER_URL`; removed entirely
along with the now-empty `environment {}` blocks
- **Add `OCI_ARTIFACT_HOST` env var** — added `OCI_ARTIFACT_HOST =
'us-docker.pkg.dev/pingcap-testing-account/hub'` to all 31 tiflash
pipeline files
- **Replace `license-eye` download** — 16 files used a hardcoded `wget`
from fileserver to fetch the binary; replaced with the standardized OCI
download script running in a dedicated `utils` container:

```groovy
// Before
wget -q -O license-eye http://fileserver.pingcap.net/download/cicd/ci-tools/license-eye_v0.4.0

// After (inside container('utils') { ... })
${WORKSPACE}/scripts/artifacts/download_pingcap_oci_artifact.sh --license-eye=v0.4.0
```

- **Pod YAML files** — added `utils` container
(`ghcr.io/pingcap-qe/cd/utils/release:v2025.10.12-7-gfdd779c`) to 14 pod
yaml files (`pod-pull_build.yaml` and `pod-merged_build.yaml` for all
affected branches), since the `tiflash-llvm-base` runner image does not
include `oras`; the license check stage now runs inside
`container('utils')`

> **Note:** The `scripts/artifacts` changes required to support
`--license-eye=VERSION` in the download script and the corresponding
upload script additions have been split into a separate PR targeting
`main`. This PR should be merged after that scripts PR lands.

## OCI Artifact Path

| Tool | OCI Reference |
|------|--------------|
| `license-eye` v0.4.0 (amd64) |
`us-docker.pkg.dev/pingcap-testing-account/hub/pingcap/third-party/license-eye:v0.4.0_linux_amd64`
|
| `license-eye` v0.4.0 (arm64) |
`us-docker.pkg.dev/pingcap-testing-account/hub/pingcap/third-party/license-eye:v0.4.0_linux_arm64`
|

Affects branches: `latest`, `release-6.1`, `release-6.5`, `release-7.1`,
`release-7.5`, `release-8.1`, `release-8.2`, `release-8.3`,
`release-8.4`, `release-8.5`, `release-9.0-beta`

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>fileserver: migrate artifacts for
pingcap/tiflash</issue_title>
> <issue_description>Replace fileserver.pingcap.net usage for
pingcap/tiflash with OCI artifacts in a standard registry.
> 
> Acceptance criteria:
> - No fileserver.pingcap.net references in jobs/pipelines for
pingcap/tiflash
> - Artifacts pulled via OCI registry with documented paths
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes PingCAP-QE/ci#4211

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
Co-authored-by: wuhuizuo <wuhuizuo@126.com>
 (commit: c981deb)