fix(verl): load Kubernetes job templates as UTF-8

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A valid UTF-8 Kubernetes Job template can fail during rollout-manager initialization on Windows with a GBK default locale. Path.read_text() uses that locale and raises UnicodeDecodeError for ordinary UTF-8 text, before rollouts can be queued.

Read the template explicitly as UTF-8. Add a real manager-initialization regression with an em dash in the template and assert the complete text retained in the rollout configuration; close the allocated client afterwards.

Validation with the frozen native Windows Python 3.12 environment:

python -m pytest tests/verl/test_agl_rollout_manager.py -q -k loads_k8s_job_template_as_utf8
python -m pytest tests/verl/test_agl_rollout_manager.py -q
python -m ruff check agentlightning/verl/agl_rollout_manager.py tests/verl/test_agl_rollout_manager.py
python -m ruff format --check agentlightning/verl/agl_rollout_manager.py tests/verl/test_agl_rollout_manager.py
python -m pre_commit run --files agentlightning/verl/agl_rollout_manager.py tests/verl/test_agl_rollout_manager.py
git diff --check

Unchanged main: the regression failed with the actual GBK UnicodeDecodeError (byte 0x94). With the fix: 1 target test and all 14 tests in the file passed. Scoped Pyright passed with 0 errors. This regression is platform-specific: systems whose default locale is already UTF-8 can pass before the fix.

No HTTP calls, model inference or GPU training were run. Ready for review based on the author-reported validation above; this maintenance pass did not rerun tests. The CLA check passed. Fork CI is awaiting maintainer approval (action_required, 0 jobs); no CI jobs have run. AI assistance was used; the one-line production change and regression were reviewed.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused encoding fix is correct and covered by an appropriate regression test.

Review effort: Balanced
Findings: None

What changed in this PR

Ensures Kubernetes Job templates load consistently as UTF-8, including on Windows systems using GBK locales.

Changes:

• Reads Job templates with explicit UTF-8 encoding.
• Adds a regression test preserving non-ASCII template text.

File	Description
agentlightning/​verl/​agl_rollout_manager.py	Explicitly decodes Kubernetes templates as UTF-8.
tests/​verl/​test_agl_rollout_manager.py	Tests UTF-8 loading and client cleanup.

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