fix(diagnostics): reject reserved type-name bindings in every module (issue 0077)

The issue-0076 reserved-type-name binding diagnostic only ran over main-file
decls, so an imported module (or the stdlib) could still declare `s2 := ...`
and reach lowering, where the address-of family loads the whole aggregate and
passes it by value to a `ptr` param — LLVM verifier abort.

Extend coverage to every compiled module: a dedicated `checkBindingNames` walk
(in semantic_diagnostics.zig) visits every var/`:=`/typed-local binding name and
function/lambda/struct-method parameter at any depth, with NO main-file filter,
descending the `namespace_decl` that a `mod :: #import` wraps so imported-module
decls are reached. It tracks each module's source_file (save/restore per node)
so the diagnostic renders against the imported module's text. Rejection still
defers to the parser's `Type.fromName` classifier; the unknown-type check (0064)
stays main-file-only. No lowering special-case; `.identifier`-only address-of
paths are unchanged.

Stdlib audit: the only reserved-name bindings under library/ were two `u1`
locals in ui/renderer.sx (UV coords) — renamed to u_min/u_max/v_min/v_max.

Regression test: examples/1120-diagnostics-imported-reserved-type-name.sx (+
companion mod.sx) — an imported `s2 := ...` now emits the clean diagnostic at
the import's declaration site (exit 1), not an LLVM abort.

Resolves issues 0076 (coverage extension) and 0077.

examples/1120-diagnostics-imported-reserved-type-name.sx

@@ -0,0 +1,16 @@
+// A value binding spelled as a reserved type name (`s2`, the `sN` arbitrary-
+// width int syntax) is rejected at its declaration site even when it lives in
+// an IMPORTED module — the reserved-name binding diagnostic covers every
+// compiled module, not just the main file. Without universal coverage the
+// binding reaches lowering and aborts LLVM verification (a loaded aggregate
+// passed by value to a `*Box` param).
+//
+// Regression (issue 0077): the imported-module facet of issue 0076. Expected:
+// one clean diagnostic pointing at the imported module's `s2 := ...`, exit 1 —
+// NOT an LLVM verifier abort.
+#import "modules/std.sx";
+mod :: #import "1120-diagnostics-imported-reserved-type-name/mod.sx";
+
+main :: () -> s32 {
+    return mod.run_imported_reserved_name();
+}

examples/1120-diagnostics-imported-reserved-type-name/mod.sx

@@ -0,0 +1,16 @@
+#import "modules/std.sx";
+
+Box :: struct { total: s64 = 0; count: s64 = 0; }
+
+update :: (self: *Box, n: s64) {
+    self.total += n;
+    self.count += 1;
+}
+
+run_imported_reserved_name :: () -> s32 {
+    s2 := Box.{ total = 0, count = 0 };
+    update(@s2, 5);
+    s2.update(7);
+    print("imported s2 total={} count={}\n", s2.total, s2.count);
+    return 0;
+}

examples/expected/1120-diagnostics-imported-reserved-type-name.exit

@@ -0,0 +1 @@
+1

examples/expected/1120-diagnostics-imported-reserved-type-name.stderr

@@ -0,0 +1,5 @@
+error: 's2' is a reserved type name and cannot be used as an identifier
+  --> examples/1120-diagnostics-imported-reserved-type-name/mod.sx:11:5
+   |
+11 |     s2 := Box.{ total = 0, count = 0 };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

examples/expected/1120-diagnostics-imported-reserved-type-name.stdout

@@ -0,0 +1 @@
+