feat: implement ZynPEG 2.0 Phase 1 - grammar IR and runtime

Phase 1 of the new PEG implementation with named bindings:

Grammar IR (crates/zyn_peg/src/grammar/):
- GrammarIR: Complete grammar representation with metadata
- PatternIR: Patterns with named bindings (name:identifier syntax)
- ActionIR: Semantic actions (Construct, HelperCall, PassThrough)
- ExprIR: Action expressions for AST construction
- Hand-written recursive descent parser for .zyn files

Runtime (crates/zyn_peg/src/runtime2/):
- ParserState: Position tracking, arena integration, bindings
- MemoCache: Packrat memoization for O(n) parsing
- Combinators: literal, optional, choice, sequence, repeat, etc.

This replaces the fragile positional $N captures with named bindings
and lays foundation for direct TypedAST code generation.

Author: darmie

crates/zyn_peg/src/grammar/ir.rs

@@ -0,0 +1,23 @@
+//! Grammar IR and Parser for ZynPEG 2.0
+//!
+//! This module provides:
+//! - `ir.rs`: Intermediate representation for grammar rules with named bindings
+//! - `parser.rs`: Parser for the new .zyn grammar syntax
+//!
+//! The new grammar syntax uses named bindings instead of positional `$N` captures:
+//!
+//! ```zyn
+//! fn_def = { "fn" ~ name:identifier ~ "(" ~ params:fn_params? ~ ")" ~ ret:type_annotation? ~ body:block }
+//!   -> TypedDeclaration::Function {
+//!       name: name.text,
+//!       params: params.unwrap_or_default(),
+//!       return_type: ret,
+//!       body: body,
+//!   }
+//! ```
+
+pub mod ir;
+pub mod parser;
+
+pub use ir::*;
+pub use parser::*;