iter 24.1: bool_to_str + str_clone runtime + codegen wiring

First iter of milestone 24 (Show + print rewire). Wires two new
heap-Str-producing primitives parallel to hs.4's int_to_str /
float_to_str:

- runtime/str.c gains ailang_bool_to_str(bool) → heap-Str "true" /
  "false" and ailang_str_clone(const char *) → memcpy'd heap-Str
  copy. Both use the existing str_alloc slab helper.
- builtins.rs + synth.rs install the two signatures lockstep with
  ret_mode: Own; str_clone carries param_modes: [Borrow].
- IR-header preamble gains two unconditional `declare ptr @...`
  lines; Emitter::lower_app gets two new arms; is_static_callee
  whitelist extends with the two names.
- Five IR snapshots regenerate for the two new declares.
- Pre-existing-drift fix: int_to_str row added to builtins.rs::list()
  (hs.4 installed env.globals entry but missed the list() row).

Substantive deviation flagged by orchestrator (DONE_WITH_CONCERNS):
builtin signatures registered in uniqueness.rs::infer_module and
linearity.rs::check_module_with_visible (8 LOC × 2 files), symmetric
to iter 23.4-prep's class-method registration in the same globals
maps. Without this fix str_clone's param_modes: [Borrow] is invisible
to the App-arg walker, src_heap walks as Position::Consume, the
scope-close ailang_rc_dec is gated off, and the
str_clone_cross_realisation_uniform_abi test's plan-literal
`frees == 3` assertion does not hold. The fix is the substantively
correct repair, not a design departure.

9 new tests: 2 builtins-install unit, 2 IR-shape unit pins, 5 E2E
(2 RC-stats, 2 stdout-smoke for both Bool branches, 1 cross-
realisation). 4 new .ail.json fixtures.

Full cargo test --workspace: 513 passed, 0 failed.
bench/compile_check.py: 24/24 stable. bench/cross_lang.py: 25/25
stable.

crates/ailang-codegen/src/synth.rs

@@ -178,6 +178,20 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
             param_modes: vec![],
             ret_mode: ParamMode::Own,
         },
+        "bool_to_str" => Type::Fn {
+            params: vec![Type::bool_()],
+            ret: Box::new(Type::str_()),
+            effects: vec![],
+            param_modes: vec![],
+            ret_mode: ParamMode::Own,
+        },
+        "str_clone" => Type::Fn {
+            params: vec![Type::str_()],
+            ret: Box::new(Type::str_()),
+            effects: vec![],
+            param_modes: vec![ParamMode::Borrow],
+            ret_mode: ParamMode::Own,
+        },
         "is_nan" => Type::Fn {
             params: vec![Type::float()],
             ret: Box::new(Type::bool_()),