ffi 2.7 green: parser accepts all seven type-introducer directive forms

Six new lexer tokens (`hash_jni_interface`, `hash_objc_class`,
`hash_objc_protocol`, `hash_swift_class`, `hash_swift_struct`,
`hash_swift_protocol`) join the existing `hash_jni_class`. All seven
share the body grammar from Phases 2.1–2.6.

AST refactored: `JniClassDecl` → `ForeignClassDecl` with a
`runtime: ForeignRuntime` enum discriminator; `JniMethodDecl` →
`ForeignMethodDecl` (with `jni_descriptor_override` renamed for
clarity since it's JNI-only); `JniFieldDecl` → `ForeignFieldDecl`;
`JniClassMember` → `ForeignClassMember`. AST variant renamed
`jni_class_decl` → `foreign_class_decl`.

`parseForeignClassDecl` takes the runtime as a parameter; the
`parseConstBinding` dispatch table now maps each of the seven
directive tokens to its `ForeignRuntime` variant via
`foreignRuntimeForCurrent`. No codegen yet — Phase 3 picks up Obj-C
runtime, Phase 4 picks up Swift. Runtime-specific body items (fields,
descriptor override) are validated at sema time in later steps.

126/126 examples green.

src/lsp/server.zig

@@ -1499,6 +1499,12 @@ pub const Server = struct {
             .hash_jni_call,
             .hash_jni_static_call,
             .hash_jni_class,
+            .hash_jni_interface,
+            .hash_objc_class,
+            .hash_objc_protocol,
+            .hash_swift_class,
+            .hash_swift_struct,
+            .hash_swift_protocol,
             .hash_extends,
             .hash_implements,
             .hash_jni_method_descriptor,