feat(lang): integer numeric-limit accessors (s64.max, u8.min, s3.max) [NL.1]

A field-like access on a builtin INTEGER type name folds to a compile-time
constant of the queried type, driven by (width, signedness) arithmetic:
  sN: min=-(2^(N-1)), max=2^(N-1)-1;  uN: min=0, max=2^N-1
for every width s1..s64 / u1..u64 (not just power-of-two), plus usize/isize.

- type_resolver.zig: extract the single width parser (parseWidthInt) reused by
  resolveNamed AND the new accessors (no second parser — issue-0083 class);
  add resolveBuiltinName / integerWidthSign / integerLimitBits / integerLimitFor.
- lower.zig: lowerNumericLimit intercept beside the error.X / Struct.CONST /
  pack-arity identifier-receiver intercepts; folds ints via constInt, emits a
  clean diagnostic for a non-numeric receiver (bool/string/void/Any/noreturn),
  falls through for floats (NL.2).
- expr_typer.zig: mirror the result type so inferExprType reports the queried type.
- program_index.zig: recognize the accessors in the comptime-int / array-dim path
  so [u8.max]T (255) / [s16.max]T (32767) work; [u64.max]T is rejected oversized.
- u64.max / usize.max stored as the all-ones bit pattern with TYPE u64 (i64 -1),
  asserted via union { u: u64; s: s64 } reinterpret.

Docs: specs.md numeric-limits subsection (formulas + result-type + u64 note);
readme.md language overview. Examples 0148 (positive) / 0149 (negative-receiver).
Unit tests for the value computation in type_resolver.test.zig.

Gate: zig build, zig build test (359/359), tests/run_examples.sh (416 ok, 0 failed).

examples/expected/0148-types-int-numeric-limits.exit

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

examples/expected/0148-types-int-numeric-limits.stderr

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+

examples/expected/0148-types-int-numeric-limits.stdout

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+s1.min=-1 s1.max=0
+s2.min=-2 s2.max=1
+s3.max=3
+u1.min=0 u1.max=1
+u2.max=3
+s8.min=-128 s8.max=127
+u8.max=255
+s32.min=-2147483648 s32.max=2147483647
+s64.max=9223372036854775807
+s64.min+1 == -(s64.max): true
+s64.min + s64.max == -1: true
+u64.max as s64 == -1: true
+usize.max as s64 == -1: true
+usize.max == u64.max: true
+isize.min == s64.min: true
+typed: m3=3 mu=255 ms=-128
+[u8.max]u8 len=255 a[254]=7
+[s16.max]u8 len=32767 b[32766]=9

examples/expected/0149-types-int-numeric-limits-errors.exit

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+1

examples/expected/0149-types-int-numeric-limits-errors.stderr

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+error: type 'bool' has no '.max' — numeric limits apply only to integer and float types
+  --> examples/0149-types-int-numeric-limits-errors.sx:14:10
+   |
+14 |     b := bool.max;
+   |          ^^^^^^^^
+
+error: field 'min' not found on type 'Any'
+  --> examples/0149-types-int-numeric-limits-errors.sx:15:10
+   |
+15 |     s := MyStruct.min;
+   |          ^^^^^^^^^^^^
+
+error: type 'void' has no '.max' — numeric limits apply only to integer and float types
+  --> examples/0149-types-int-numeric-limits-errors.sx:16:10
+   |
+16 |     v := void.max;
+   |          ^^^^^^^^

examples/expected/0149-types-int-numeric-limits-errors.stdout

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+