feat: Add haxe_zyntax_runtime crate and SDK development plan

- Add haxe_zyntax_runtime crate with Haxe-specific runtime functions
  - trace() functions for strings, ints, floats, bools
  - DynamicValue trace support with type dispatch
  - ZRTL plugin exports for dynamic loading
- Add verified SDK development plan (docs/plan-zpack-sdk-stdlib.md)
  - Identified actual gaps: string format inconsistency, iterator protocol,
    method dispatch, test harness, runtime reflection API
  - Corrected false claims: generic reification, memory hooks, Result/Option
    types already exist in SDK

Author: darmie

crates/haxe_zyntax_runtime/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "haxe_zyntax_runtime"
+version = "0.1.0"
+edition = "2021"
+description = "Haxe-specific runtime for Zyntax compiler"
+
+[lib]
+# cdylib: Dynamic library for runtime loading (.so/.dylib/.dll)
+# rlib: Rust library for static linking within Rust
+# staticlib: C-compatible static library (.a) for AOT linking
+crate-type = ["cdylib", "rlib", "staticlib"]
+
+[dependencies]
+libc = "0.2"
+zyntax_compiler = { path = "../compiler" }
+zyntax_plugin_macros = { path = "../zyntax_plugin_macros" }
+inventory = "0.3"