refactor(ffi-linkage): Phase 9.3 — purge 'foreign' from comments (src caps + examples + docs)

src/: ~21 capital-Foreign comments the case-sensitive verify grep missed
(Foreign-class→Runtime-class, Foreign path→Runtime path, Foreign decls→Extern decls,
FOREIGN function→extern function) across calls/inst/ffi_objc/jni_descriptor/emit_llvm/
c_import/lower.*/ops. src 'foreign' now = ONLY the hash_foreign token + 4 rejection
messages (9.0-delete targets). examples/*.sx comments → extern/runtime-class (1219
stdout regen; KEPT 1176). docs/inline-asm-design + debugger purged. Comments only —
no build impact. 9.0 ratified: DELETE hash_foreign token next.

examples/1229-ffi-extern-cvariadic.sx

@@ -1,12 +1,12 @@
 // `extern` C-variadic tail: a trailing `..args: []T` on an `extern` fn
-// maps to the C calling convention's `...`, exactly like its `#foreign`
+// maps to the C calling convention's `...`, exactly like its `extern`
 // twin (example 1218). Extras at the call site pass through the variadic
 // slot with standard default argument promotion (i8/i16/bool → i32,
 // f32 → f64), NOT packed into an sx slice.
 //
 // Regression (FFI-linkage Part B): the `is_variadic` drop in
 // `declareFunction` + the call-site early-out in `packVariadicCallArgs`
-// were gated on `#foreign` only, so a migrated variadic `extern` lost
+// were gated on `extern` only, so a migrated variadic `extern` lost
 // its `...` tail and slice-packed the extras (garbage at the C ABI).
 
 #import "modules/std.sx";