ffi 2.1: parser accepts Foo :: #jni_class("path") { } opaque form

New `hash_jni_class` token + lexer entry, `JniClassDecl` AST node
(alias + java path; body deferred to 2.2+), `parseJniClassDecl`
consuming `("...") { }` and rejecting non-empty bodies for now.
Sema registers the alias as a type_alias symbol; LSP classifies
the directive as a keyword. The 2.0 xfail snapshot flips to
`parse-only ok`, exit 0.

120/120 examples green; zig test clean.

src/lsp/server.zig

@@ -1498,6 +1498,7 @@ pub const Server = struct {
             .hash_objc_call,
             .hash_jni_call,
             .hash_jni_static_call,
+            .hash_jni_class,
             => ST.keyword,
 
             .kw_f32, .kw_f64, .kw_Type, .kw_Self => ST.type_,