fix: preserve expression value types in json bodies

[re-pixel]

Resolves #4499

Preserves expression result types inside JSON request bodies for the HTTP action. Whole-value expressions in object/JSON fields now resolve to their native types, so numbers and booleans stay as JSON numbers/booleans, while partial string templates still render as strings.

[superplanehq-integration]

👋 Commands for maintainers:

• /sp start - Start an ephemeral machine (takes ~30s)
• /sp stop - Stop a running machine (auto-executed on pr close)

[superplane-gh-integration-9000]

PR Risk Review

Risk: 42/100 (medium)
Review approved: Yes
Check passed: Yes

Summary

This PR fixes type preservation for expression values in JSON bodies by adding type-aware resolution for object, number, and boolean fields, with comprehensive tests covering the key scenarios.

Concerns

• The refactoring of resolveListItems to delegate to resolveFieldValue changes behavior for existing list resolution paths - could have subtle regressions for list items that aren't objects/numbers/bools
• The resolveObjectString function attempts JSON decoding on any string that doesn't resolve to a non-string type, which could cause unexpected failures for string fields that happen to look like JSON
• The unwrapExpressionTemplate function uses a regex match that requires the entire trimmed string to be a single expression - edge cases with whitespace or multiple expressions on one line should be verified
• No integration tests were added to verify end-to-end behavior with actual pipeline execution

[superplane-gh-integration-9000]

PR Risk Review

Risk: 50/100 (medium)
Review approved: No
Check passed: No

Summary

Could not parse Claude review JSON.

Concerns

• Based on my detailed review, I've analyzed the diff in:
• pkg/workers/contexts/node_configuration_builder.go (~200 new lines)
• pkg/workers/contexts/node_configuration_builder_test.go (2 new unit tests)
• pkg/components/http/http_test.go (1 new integration test)

Key observations:

1. Bug fixed: Previously, a template like "{{ previous().weight }}" inside an Object/Number/Bool field would be stringified ("0.1" instead of 0.1), causing wrong JSON serialization in HTTP bodies and ot