refactor(ir): add ResolveEnv + TypeResolver shell; own primitives + compounds (A2.1)

Architecture phase A2.1 -- behavior-preserving. Introduce src/ir/type_resolver.zig
as the canonical AST-type-node -> TypeId resolver (Principle 1), starting with:

- ResolveEnv: the explicit resolution-context shape (Principle 2) -- type/pack/
  comptime bindings + target_type. Defined now; consumed as A2.2/A2.3 move the
  cases that need it.
- TypeResolver.resolvePrimitive(name): the builtin keyword table, MOVED here from
  type_bridge.resolveTypePrimitive (now a re-export -> single source; its 7
  callers are unaffected; no import cycle).
- TypeResolver.resolveCompound(node, inner): the structural compound types
  *T / [*]T / []T / ?T / [N]T. Element types recurse via inner.resolveInner (an
  anytype callback) so generic structs / bindings in element position keep their
  full stateful resolution.

Lowering.resolveTypeWithBindings duplicated the 5 simple compounds across its
bindings and no-bindings blocks (10 arms). Both are replaced with a single
self.typeResolver().resolveCompound(node, self) delegation; adds
Lowering.resolveInner (recursion hook) + typeResolver() (by-value view).

Deliberately deferred: tuples, closures, and function types stay on the existing
pack-aware helpers (resolveClosure/Tuple/FunctionTypeWithBindings); A2.3 owns
their pack-projection logic.

Tests: src/ir/type_resolver.test.zig (resolvePrimitive keyword/null cases;
resolveCompound for all 5 + null for non-compound; ResolveEnv defaults), wired
into the ir.zig barrel.

No new fallback path; no duplicate truth. Gate green: zig build, zig build test,
bash tests/run_examples.sh (350 passed, 0 failed). lower.zig 19393 -> 19372.

src/ir/ir.zig

@@ -5,6 +5,7 @@ pub const print = @import("print.zig");
 pub const interp = @import("interp.zig");
 pub const lower = @import("lower.zig");
 pub const program_index = @import("program_index.zig");
+pub const type_resolver = @import("type_resolver.zig");
 
 pub const TypeId = types.TypeId;
 pub const TypeInfo = types.TypeInfo;
@@ -32,6 +33,8 @@ pub const Interpreter = interp.Interpreter;
 pub const Value = interp.Value;
 pub const Lowering = lower.Lowering;
 pub const ProgramIndex = program_index.ProgramIndex;
+pub const TypeResolver = type_resolver.TypeResolver;
+pub const ResolveEnv = type_resolver.ResolveEnv;
 
 pub const compiler_hooks = @import("compiler_hooks.zig");
 pub const emit_llvm = @import("emit_llvm.zig");
@@ -51,6 +54,7 @@ pub const print_tests = @import("print.test.zig");
 pub const interp_tests = @import("interp.test.zig");
 pub const lower_tests = @import("lower.test.zig");
 pub const program_index_tests = @import("program_index.test.zig");
+pub const type_resolver_tests = @import("type_resolver.test.zig");
 pub const type_bridge_tests = @import("type_bridge.test.zig");
 pub const emit_llvm_tests = @import("emit_llvm.test.zig");
 pub const jni_descriptor_tests = @import("jni_descriptor.test.zig");