Remove @PlaydateMain macro and SwiftSyntax dependency

[finnvoor]

Summary

• Remove the @PlaydateMain macro and PlaydateKitMacros target
• Drop the SwiftSyntax package dependency entirely
• Restore manual entry.swift event handler boilerplate in examples

Motivation

SwiftSyntax is a large dependency that significantly increases build times for all downstream consumers of PlaydateKit. It's also tightly coupled to specific Swift compiler versions, which causes build issues — particularly when using snapshot toolchains or Xcode with non-standard toolchain configurations.

The @PlaydateMain macro only eliminated a small amount of event handler boilerplate (~18 lines per game). Restoring this boilerplate is a worthwhile tradeoff to avoid the build time and compatibility cost of SwiftSyntax.