fix(ir): validate const-expression typed module-const initializers [F0.7]

Attempt 1 rejected only LITERAL initializers that mismatch a typed module
const's annotation; a const-EXPRESSION initializer escaped, so the same
issue-0088 root remained for `M :: 2; N : string : M + 2` — accepted at exit 0,
folding `[N]s64` to 4 and printing N as an integer.

Root cause: `registerTypedModuleConst` validated only the enumerated literal
node kinds; any other kind fell through to `else => {}`, and pass 0
pre-registers binary_op/unary_op consts as a `.s64` placeholder that was never
reconciled with the annotation.

Fix — validate by TYPE, not by node kind:
- lower.zig: `registerTypedModuleConst` now covers literals AND const-expressions
  (binary_op/unary_op) through one path. `typedConstInitFits` keeps the literal
  arms and routes any non-literal through the new `constExprInitFits`, which
  compares the initializer's INFERRED type (`inferExprType`, the existing
  type-inference facility — no second const evaluator) to the annotation with the
  same integer/float compatibility. A mismatch emits the `type mismatch` diagnostic
  (a const-expression is described by its inferred type, e.g. "an integer
  expression") and evicts the pass-0 placeholder; a match registers the const at
  its resolved annotation type (the same `put` the literal path always did), so a
  const-expression folds and emits at its declared type.
- `literalKindName` → `initializerDescription` (+ `constExprDescription`) so the
  message is accurate for both a literal and a const-expression initializer.

Regression:
- examples/1143: extended with `E : string : M + 2` and `V : string : -M`
  (const-expr mismatches → exit 1, pinned diagnostics).
- examples/0162: extended with `KE : s64 : M + 2` (used as a count + printed) and
  `WE : f32 : M + 2` (over-rejection guard — valid const-exprs still work).
- program_index.test.zig: count-gate test extended with a binary_op value node
  declared `string` (must not fold as a count).

Docs: specs.md §3 + readme.md generalized from "initializer literal" to cover
constant expressions; issues/0088 RESOLVED banner updated.

examples/expected/0162-types-typed-module-const-roundtrip.stdout

@@ -2,3 +2,4 @@ K=4 len=4 a0=10 a3=40
 W=800.000000 PI=3.141590
 S=hi
 P_is_null=true
+KE=4 len=4 WE=4.000000

examples/expected/1143-diagnostics-typed-module-const-mismatch.stderr

@@ -1,23 +1,35 @@
 error: type mismatch: constant 'N' is declared 'string' but its initializer is an integer literal
-  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:13:14
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:18:14
    |
-13 | N : string : 4;     // integer literal where a string is annotated
+18 | N : string : 4;        // integer literal where a string is annotated
    |              ^
 
 error: type mismatch: constant 'F' is declared 's64' but its initializer is a string literal
-  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:14:14
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:19:14
    |
-14 | F : s64    : "x";   // string literal where an integer is annotated
+19 | F : s64    : "x";      // string literal where an integer is annotated
    |              ^^^
 
 error: type mismatch: constant 'B' is declared 's64' but its initializer is a boolean literal
-  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:15:14
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:20:14
    |
-15 | B : s64    : true;  // boolean literal where an integer is annotated
+20 | B : s64    : true;     // boolean literal where an integer is annotated
    |              ^^^^
 
 error: type mismatch: constant 'G' is declared 's64' but its initializer is a float literal
-  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:16:14
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:21:14
    |
-16 | G : s64    : 1.5;   // float literal where an integer is annotated
+21 | G : s64    : 1.5;      // float literal where an integer is annotated
    |              ^^^
+
+error: type mismatch: constant 'E' is declared 'string' but its initializer is an integer expression
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:22:14
+   |
+22 | E : string : M + 2;    // integer EXPRESSION where a string is annotated
+   |              ^^^^^
+
+error: type mismatch: constant 'V' is declared 'string' but its initializer is an integer expression
+  --> examples/1143-diagnostics-typed-module-const-mismatch.sx:23:14
+   |
+23 | V : string : -M;       // integer (unary) expression where a string is annotated
+   |              ^^