🔧 Fix peek expression terminator issues and add ternary operator support

- Fix LLVM IR terminator missing in peek expression entry blocks
- Add proper jump instructions between peek blocks
- Implement ternary operator (? :) as syntactic sugar for peek
- Update Python LLVM externcall handling for improved compatibility
- Add comprehensive test cases for peek and ternary expressions
- Update language guide with ternary operator documentation

ChatGPTが頑張って修正してくれたにゃ！🐱

Co-Authored-By: ChatGPT <noreply@openai.com>

apps/tests/ternary_nested.nyash

@@ -0,0 +1,10 @@
+static box Main {
+  main(args) {
+    local a = 3
+    local b = 5
+    // Nested ternary: should evaluate to 50
+    local v = (a < b) ? ((b < 0) ? 40 : 50) : 60
+    return v
+  }
+}
+