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/sema.zig

@@ -910,6 +910,12 @@ pub const Analyzer = struct {
             .foreign_class_decl => |fd| {
                 try self.addSymbol(fd.name, .type_alias, null, node.span);
             },
+            .jni_env_block => |eb| {
+                try self.analyzeNode(eb.env);
+                try self.pushScope();
+                try self.analyzeNode(eb.body);
+                self.popScope();
+            },
             .impl_block => |ib| {
                 // Each impl block gets its own scope so methods don't conflict across impls
                 try self.pushScope();
@@ -1311,6 +1317,10 @@ pub fn findNodeAtOffset(node: *Node, offset: u32) ?*Node {
         .closure_type_expr,
         .foreign_class_decl,
         => {},
+        .jni_env_block => |eb| {
+            if (findNodeAtOffset(eb.env, offset)) |found| return found;
+            if (findNodeAtOffset(eb.body, offset)) |found| return found;
+        },
         .struct_decl => |sd| {
             for (sd.methods) |method_node| {
                 if (findNodeAtOffset(method_node, offset)) |found| return found;