Frends.JSON.Handlebars: compliance fixes — net8, static class, Options param, Error result

[Copilot]

Resolves task analyzer findings (FT0004, FT0007, FT0011), upgrades target framework to net8.0, and adds standard error-handling support.

Changes

• net8.0 — Both main and test projects retargeted from net6.0
• Static class (FT0004) — JSON class is now static
• Options parameter (FT0007) — New Options class added; Handlebars() now accepts it as a [PropertyTab] parameter with ThrowErrorOnFailure (default true) and ErrorMessageOnFailure
• Error property on Result (FT0011) — New Error class (Message, AdditionalInfo); Result gains an Error property populated on failure
• ErrorHandler helper — Helpers/ErrorHandler.cs with standard ex.Handle(options) extension; main method body wrapped in try/catch
• Version bumped to 1.3.0

Updated call signature

// Before
JSON.Handlebars(input, cancellationToken)

// After
JSON.Handlebars(input, options, cancellationToken)

Error handling behavior

var options = new Options { ThrowErrorOnFailure = false };
var result = JSON.Handlebars(input, options, ct);
// result.Success == false, result.Error.Message contains the reason