lang: extend operand-type check to ordering + bitwise/shift (issue 0055 follow-up)

The arithmetic-only check from the previous commit shared a hole with the
comparison and bitwise/shift ops: lowerBinaryOp derives the result type
from the LHS, so `s64 < string` fed mismatched types to `icmp` (LLVM
verifier failure) and `s64 & string` reinterpreted the string's bytes.

Add isOrderingOperand (numeric / enum / pointer / bool / vector) and
isBitwiseOperand (integer / enum / bool / vector), and route `< <= > >=`
and `& | ^ << >>` through them alongside the existing arithmetic check, all
sharing one diagnostic + placeholder-sentinel path. Flags-enum bitwise
(`.read | .write`, `perm & .read`), enum/pointer comparison, and int
literals stay legal (50-smoke unaffected).

Equality `== / !=` is deliberately left unchecked — its path is heavily
special-cased (str_eq, Any unbox, optional == null); folding a check in
without regressing those is a separate change, noted in the issue.

Regression test renamed arith→binop and broadened to cover `+ * < & <<`
against a string operand: examples/214-binop-operand-type-check.sx.

tests/expected/214-arith-operand-type-check.txt

@@ -1,11 +0,0 @@
-error: cannot apply '+' to operands of type 's64' and 'string'
-  --> /Users/agra/projects/sx/examples/214-arith-operand-type-check.sx:12:10
-   |
-12 |     x := n + s;     // s64 + string — rejected
-   |          ^
-
-error: cannot apply '*' to operands of type 'string' and 's64'
-  --> /Users/agra/projects/sx/examples/214-arith-operand-type-check.sx:13:10
-   |
-13 |     y := s * n;     // string * s64 — rejected (non-numeric LHS too)
-   |          ^

tests/expected/214-binop-operand-type-check.txt

@@ -0,0 +1,29 @@
+error: cannot apply '+' to operands of type 's64' and 'string'
+  --> /Users/agra/projects/sx/examples/214-binop-operand-type-check.sx:19:10
+   |
+19 |     a := n + s;      // arithmetic: s64 + string
+   |          ^
+
+error: cannot apply '*' to operands of type 'string' and 's64'
+  --> /Users/agra/projects/sx/examples/214-binop-operand-type-check.sx:20:10
+   |
+20 |     b := s * n;      // arithmetic: non-numeric LHS (string * s64)
+   |          ^
+
+error: cannot apply '<' to operands of type 's64' and 'string'
+  --> /Users/agra/projects/sx/examples/214-binop-operand-type-check.sx:21:10
+   |
+21 |     c := n < s;      // ordering:   s64 < string
+   |          ^
+
+error: cannot apply '&' to operands of type 's64' and 'string'
+  --> /Users/agra/projects/sx/examples/214-binop-operand-type-check.sx:22:10
+   |
+22 |     d := n & s;      // bitwise:    s64 & string
+   |          ^
+
+error: cannot apply '<<' to operands of type 's64' and 'string'
+  --> /Users/agra/projects/sx/examples/214-binop-operand-type-check.sx:23:10
+   |
+23 |     e := n << s;     // shift:      s64 << string
+   |          ^