docs(spec): split range bounds from counts; pin inline-for range semantics (0083)

specs.md lumped `inline for` / `for` range bounds in with counts (array
dimension, Vector lane count, generic value-param count) under the
count negative-rejection rule. A range bound is a range ENDPOINT, not a
count: negative endpoints are valid and an empty/inverted range runs zero
iterations. The compiler already implements this correctly (Agra ruling:
spec-text bug, no code change).

- specs.md: counts and range bounds are now described separately. Counts
  reject negatives; bounds accept any compile-time integer (negatives
  valid, integral floats fold) but still reject a non-integral float
  because the loop cursor must be an integer.
- examples/0612-comptime-inline-for-range-bounds.sx: `inline for -2..1`
  and `for -2..1` both sum -3; `inline for 0..(-2.0)` runs zero
  iterations (empty range). Runtime/comptime parity asserted.
- examples/1138-diagnostics-inline-for-non-integral-bound.sx: a
  non-integral float bound `inline for 0..4.5` is a clean diagnostic,
  exit 1 (must-be-integer still applies to bounds).

Count consumers (1132/1133/1134/1135) unchanged and green.

examples/expected/0612-comptime-inline-for-range-bounds.exit

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

examples/expected/0612-comptime-inline-for-range-bounds.stderr

@@ -0,0 +1 @@
+

examples/expected/0612-comptime-inline-for-range-bounds.stdout

@@ -0,0 +1,3 @@
+inline for -2..1 sum = -3
+for -2..1 sum = -3
+inline for 0..(-2.0) sum = 0

examples/expected/1138-diagnostics-inline-for-non-integral-bound.exit

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

examples/expected/1138-diagnostics-inline-for-non-integral-bound.stderr

@@ -0,0 +1,5 @@
+error: inline for: range end is not a compile-time integer
+  --> examples/1138-diagnostics-inline-for-non-integral-bound.sx:12:19
+   |
+12 |     inline for 0..4.5: (i) { s += i; }
+   |                   ^^^

examples/expected/1138-diagnostics-inline-for-non-integral-bound.stdout

@@ -0,0 +1 @@
+