fix(instances): accept decimal values in memory and disk strings

[laolusrael]

Summary

Fixes PUT /api/instances/{name}/resources rejecting valid decimal memory/disk values like "4.0G" and "25.0G".

Problem

parseMemoryString used strconv.ParseInt, which fails on strings containing decimal points (e.g., "4.0"). When the frontend sent "memory": "4.0G", the endpoint returned:

{"error":"invalid_request","message":"invalid memory format"}

Fix

• Changed strconv.ParseInt to strconv.ParseFloat in parseMemoryString
• Result is cast to int64 after multiplying by the unit multiplier

Tests Added

• TestUpdateResources_DecimalMemoryFormat — verifies "4.0G" is accepted
• TestParseMemoryString — unit tests for parsing: 1G, 4.0G, 25.0G, 512M, 2.5G, 1024, empty string

Test Results

• go test -tags ci ./... — Pass