fix: preserve single-run input variable types

[Jingyi-Dify]

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Summary

Fixes single-step run inputs so referenced variables keep their expected input types instead of falling back to text inputs.

Change List

• Use value_type as a fallback when a single-run variable cannot be resolved from workflow output metadata.
• Resolve sys.* variables by their full variable name across available workflow variable groups.
• Preserve number input behavior for system variables such as sys.timestamp and sys.dialogue_count.

Testing

• Verified the diff is limited to web/app/components/workflow/nodes/_base/hooks/use-one-step-run.ts.
• Manually checked the affected single-run input paths for normal variables and system variables.

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

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.73%. Comparing base (574d586) to head (656d9e2).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
...nts/workflow/nodes/_base/hooks/use-one-step-run.ts	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #35710      +/-   ##
==========================================
+ Coverage   85.68%   85.73%   +0.04%     
==========================================
  Files        4460     4458       -2     
  Lines      209183   208973     -210     
  Branches    39040    39040              
==========================================
- Hits       179241   179163      -78     
+ Misses      26779    26645     -134     
- Partials     3163     3165       +2     

Flag	Coverage Δ
dify-ui	93.01% <ø> (ø)
web	86.60% <85.71%> (+0.12%)	⬆️

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[lyzno1]

No blocking issues found.

Verified locally:

• pnpm test app/components/workflow/nodes/_base/hooks/__tests__/use-one-step-run.spec.ts
• pnpm type-check
• pnpm exec eslint app/components/workflow/nodes/_base/hooks/__tests__/use-one-step-run.spec.ts

Small non-blocking suggestion: consider adding one more fallback test for an unresolved variable with options, asserting it becomes InputVarType.select and preserves options. The implementation already handles this path, but the current spec only covers the number fallback.