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/0729-modules-flat-same-name-foreign/a.sx

@@ -1,5 +1,5 @@
-// One of two flat authors of `absval`, a `#foreign` libc binding. A consumer
+// One of two flat authors of `absval`, a `extern` libc binding. A consumer
 // flat-importing BOTH must NOT see this as an ambiguous bare-call collision —
-// foreign authors are never rerouted by the bare-call resolver, so the call
-// falls to the existing first-wins foreign dispatch.
+// extern authors are never rerouted by the bare-call resolver, so the call
+// falls to the existing first-wins extern dispatch.
 absval :: (n: i32) -> i32 extern libc "abs";

examples/0729-modules-flat-same-name-foreign/b.sx

@@ -1,2 +1,2 @@
-// The second flat author of `absval` — the identical `#foreign` libc binding.
+// The second flat author of `absval` — the identical `extern` libc binding.
 absval :: (n: i32) -> i32 extern libc "abs";