P5.7 Step E: fix issue 0141 (reject silent [*]T -> []T coercion); land regression

The 0141 repro relied on a silent-wrong coercion: passing List.items (a
[*]T many-pointer, no length) to a []T parameter passed the bare 8-byte
pointer into a 16-byte {ptr,len} slot — garbage .len, at comptime a segfault
in the VM slice decoder (decodeMemberSlice), at runtime an LLVM verify failure.

Fix (root cause): classify [*]T -> []T as many_to_slice_reject in
conversions.zig and emit a build-gating diagnostic in coerce.zig telling the
user to slice with a length (ptr[0..len]). Guard runComptimeTypeFunc to skip
VM eval once diagnostics.hasErrors() — a type-fn body that failed coercion
holds malformed comptime data (a real host Addr) that would fault the VM's
Ref-level guards.

Land the corrected feature as examples/0640 (List-grown comptime enum via
vs.items[0..vs.len] -> green=7) and the rejection as
examples/1183-diagnostics-many-pointer-to-slice-rejected. Mark issue 0141
RESOLVED.

708/0 corpus + 476/476 unit.

src/ir/lower/comptime.zig

@@ -504,6 +504,15 @@ pub fn runComptimeTypeFunc(self: *Lowering, func_id: FuncId, span: ast.Span) ?Ty
         }
     }
 
+    // If lowering this type-fn's BODY already emitted an error (e.g. a rejected
+    // coercion like `[*]T → []T`, issue 0141), the function holds malformed IR —
+    // a slice value that is really a bare 8-byte pointer, etc. Running the VM on it
+    // would dereference garbage (a comptime Addr is a real host pointer, so a bad
+    // data pointer FAULTS, defeating the VM's bail-not-crash guards which only catch
+    // malformed Refs, not malformed comptime DATA). The user's real diagnostic is
+    // already on the list; skip the eval and let `hasErrors()` abort the build.
+    if (self.diagnostics) |d| if (d.hasErrors()) return null;
+
     // The comptime VM is the SOLE evaluator (P5.7) — no legacy fallback. A
     // type-fn runs on the VM; a bail is ALWAYS a build-gating diagnostic, never a
     // fallback. The VM is hardened against malformed lowering-time IR (it BAILS,