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.
Today's parser doesn't recognize #jni_class as a hash directive
after `::`, so it falls through to expression parsing and errors
at the `#` token. Step 2.1 extends parseConstBinding to accept
the directive (opaque on empty body) and re-snapshots this file
to green.