fix: always send variables field in function run/schedule requests

[giordano-lucas]

Summary

• Always include variables field (as {} when empty) in the functions run request body — the API now requires it
• Set Variables to an empty map on functions schedule request body so it's serialized instead of omitted

Fixes 3 integration test failures: TestFunctionIDResolution, TestFunctionRun, TestFunctionsScheduleAndUnschedule

Test plan

• Verify notte functions run works without --var/--vars flags
• Verify notte functions run --var key=value still works
• Verify notte functions schedule works
• Integration tests pass in CI

🤖 Generated with Claude Code

Greptile Summary

This PR fixes two API serialization issues where required fields were being omitted from request bodies, causing integration test failures.

• runFunctionRun: Removes the len(variables) > 0 guard so "variables" is always serialized (as {} when no variables are provided), matching the API's requirement.
• runFunctionSchedule: Initializes Variables to &emptyVars (a pointer to an empty map[string]interface{}) so the field is serialized as "variables": {} instead of being omitted due to the omitempty JSON tag on the *map[string]interface{} pointer.

Confidence Score: 5/5

• This PR is safe to merge — it makes minimal, targeted fixes to ensure required API fields are always serialized.
• The changes are small, well-scoped, and correct. variables in runFunctionRun was already initialized to an empty map, so always including it is a safe no-op when no variables are provided. In runFunctionSchedule, assigning a non-nil pointer to Variables correctly forces JSON serialization despite the omitempty tag. No logic is altered beyond ensuring the fields are present in the serialized body.
• No files require special attention.

Important Files Changed

Filename	Overview
internal/cmd/functions.go	Always includes variables field in function run request body and initializes Variables to an empty map pointer for schedule requests so it is serialized rather than omitted.

_{Last reviewed commit: 2641b15}