chore(deps): pin uv to 0.12.5 across project, CI, and Docker

[TATP-233]

Summary

Pin the uv toolchain version so lockfile output stops depending on which uv release a contributor or runner happens to have. Motivation: while bumping unilab-rl in #1655, a plain uv lock with local uv 0.12.5 rewrote ~370 lines of uv.lock in pure formatting churn (marker simplification, size/upload-time backfill) on top of the one-line version change, because the committed locks were last emitted by an older uv and nothing in the repo constrained the uv version.

Changes:

• pyproject.toml / pyproject.rocm.toml: [tool.uv] required-version = "==0.12.5" — uv now hard-errors with a clear message on any other version, for every contributor and every make sync* path (including the ROCm box, whose uv was 0.11.33)
• .github/workflows/ci.yml (6 jobs), docs.yml (2), release.yml (1): setup-uv@v8.0.0 now pins version: "0.12.5" instead of floating on latest
• Dockerfile: installer URL pinned to https://astral.sh/uv/0.12.5/install.sh
• docs/sphinx/source/{en,zh_CN}/1-getting_started/2-installation.md: install instructions use the pinned installer and mention required-version

No lockfile renormalization is included, deliberately: uv lock preserves the existing formatting of untouched entries, so the old-format entries are stable as-is, and forcing a full regeneration (rm uv.lock && uv lock) would also upgrade unrelated package versions. With the version pinned, future lock diffs stay minimal without a churn-heavy rewrite.

Linked Work

• Issue: none — follow-up tooling hardening from chore(deps): bump unilab-rl to 1.4.1 #1655 review discussion
• Base branch: main

Validation

• make test-all passed on the final local head before this PR was created or updated — N/A for behavior: no src//tests/ changes; CI/tooling-only. Focused checks below.
• Additional task-specific validation listed below

Commands actually run (final local head a9079fd):

uv lock --check                                            # main lock OK under pinned 0.12.5
uv run pytest tests/scripts/test_check_docs.py -q          # 19 passed
cd docs/sphinx && UNILAB_DOCS_SKIP_AUTODOC=1 uv run --no-project \
  --with-requirements requirements.txt sphinx-build -b html -n source build/html   # success, no new warnings

# On the ROCm host (ssh amd, /home/unilab/unilabsim/UniLab, uv self-updated 0.11.33 -> 0.12.5):
git worktree add /tmp/unilab-pin-check origin/chore/pin-uv-0.12.5 --detach
uv lock --check                                            # main lock OK (240 packages)
# with pyproject.rocm.toml + uv.rocm.lock swapped in per the make sync-rocm flow:
uv lock --check                                            # ROCm lock OK (177 packages)

Remote CI route:

• Base main: current-head CI recorded below once the run starts.

Impact

• Backend impact: none
• Platform impact: both (all contributors now need uv 0.12.5; required-version emits an explicit error otherwise)
• Training effect expected: no

Artifacts

• N/A

Checklist

• Added or updated tests where needed — N/A, no behavior change
• Updated docs if behavior or workflow changed — installation pages (en + zh_CN) now install the pinned uv
• Linked the driving issue — none; follows chore(deps): bump unilab-rl to 1.4.1 #1655
• Noted any follow-up work explicitly — ROCm host uv upgraded to 0.12.5 via uv self update; any other dev machines will be prompted by required-version to match