refactor(ffi-linkage): Phase 9.3 — purge remaining 'foreign' from library/docs/example comments

Capital-Foreign + stale-identifier comment refs: library (Foreign Java types→Runtime,
foreign-class→runtime-class, foreign_class_map→runtime_class_map); docs/debugger
(foreign call→extern call); docs/fork-c ledger (foreign_class_map, protocol/foreign→
runtime-class); docs/inline-asm-design Deviation-6 obsolete #foreign-vs-extern design
RESOLVED to the landed extern/export reality; example comments (parseForeignClassDecl→
parseRuntimeClassDecl, checkForeignRefs→checkExternRefs, Foreign decls→Extern). Docs/
comments only — no build impact.

examples/0415-protocols-protocols.sx

@@ -193,9 +193,9 @@ sm_first :: (a: i32, b: i32) -> (i32, !) {
     return v;
 }
 
-// --- Foreign function binding ---
+// --- Extern function binding ---
 
-// --- Foreign function binding ---
+// --- Extern function binding ---
 libc :: #library "c";
 
 c_abs :: (n: i32) -> i32 extern libc "abs";