ffi 2.16a green: parser + AST + sema for #jni_env(env) { body }

New `hash_jni_env` lexer token; `parsePrimary` dispatches to a small
`parseJniEnvBlock` that consumes `(env) { body }` and returns a new
`JniEnvBlock` AST node (env_expr + body block).

Sema's analyzeNode arm recurses into env + body inside a pushed
scope; findNodeAtOffset descends through both children for go-to-
definition.

Lowering treats it as a syntactic wrapper around the block: env is
evaluated for side effects, body lowers as a normal block. The TL
push/pop semantics (synthesizing the env stack so `#jni_call`'s env
arg can become optional) land in 2.16b.

`expectSemicolonAfter` recognises `jni_env_block` as block-form so
statement-position uses don't need a trailing `;` — matches `if` /
`while` / `for` / bare blocks.

Test runs through the block body and prints expected output; xfail
snapshot flips to green. 127/127 examples green.

src/token.zig

@@ -125,6 +125,7 @@ pub const Tag = enum {
     hash_extends, // `#extends Alias;` inside a foreign-class body
     hash_implements, // `#implements Alias;` inside a foreign-class body
     hash_jni_method_descriptor, // `#jni_method_descriptor("(Sig)Ret")` per-method JNI descriptor override
+    hash_jni_env, // `#jni_env(env) { body }` block-form env-scoping intrinsic
     triple_minus, // ---
 
     // Special