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/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 @@
+