refactor(ffi-linkage): Phase 9.3/9.4 — purge 'foreign' from issues/*.md; GATE PASS

Rewrote 20 issue writeups to the extern/runtime-class vocabulary (#foreign→extern,
foreign_class_map→runtime_class_map, parseForeignClassDecl→parseRuntimeClassDecl,
findForeignMethodInChain→findRuntimeMethodInChain, dedupeForeignSymbol→
dedupeExternSymbol, is_foreign_c_api→is_extern_c_api, stale filename refs to the
renamed examples, foreign-class→runtime-class, bare foreign→extern). Renamed
issues/0043-…-foreign-class-…→…-runtime-class-….

PHASE 9 COMPLETE — 9.4 GATE PASSES: zero 'foreign' across src/library/examples/
issues/docs/editors/specs/readme/CLAUDE, excluding only the SQLite API constant
SQLITE_CONSTRAINT_FOREIGNKEY + vendored sqlite3.c/.h (upstream third-party).
Suite green (644 corpus / 443 unit, 0 failed).

issues/0071-global-initializer-module-const-silent-zero.md

@@ -84,7 +84,7 @@ Likely fix:
   a diagnostic instead of returning `null` / zero-initializing.
 - Do not regress issue 0070: `A :: B; B :: i32; g : A = 7;` and
   `K : A : 35;` must still resolve through the converged alias map.
-- Preserve literal, array literal, struct literal, and foreign-global behavior.
+- Preserve literal, array literal, struct literal, and extern-global behavior.
 
 Verification:
 - Add a focused regression, likely in the `01xx` types block: