fix: pipeline template render

[FFXN]

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Summary

Due to multiple commits in sessionmaker, the transaction is closed early.
When creating a pipeline using a template, the DataSet ID is returned as empty, causing the render to fail.

Screenshots

Before	After
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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	0.00%	43.68%	+43.68%
Strict coverage	0.00%	43.21%	+43.21%
Typed symbols	0	22,034	+22,034
Untyped symbols	0	28,717	+28,717
Modules	0	2552	+2,552

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.90%. Comparing base (d1d1903) to head (1a0c8f6).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #36168      +/-   ##
==========================================
+ Coverage   85.89%   85.90%   +0.01%     
==========================================
  Files        4454     4456       +2     
  Lines      210783   210739      -44     
  Branches    39427    39404      -23     
==========================================
- Hits       181047   181035      -12     
+ Misses      26515    26482      -33     
- Partials     3221     3222       +1     

Flag	Coverage Δ
api	85.35% <100.00%> (+<0.01%)	⬆️

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