fix: make all example programs work correctly

- Add string concatenation support to + operator in typechecker
- Register ADT constructors in both type environment and interpreter
- Bind handlers as values so they can be referenced in run...with
- Fix effect checking to use subset instead of exact match
- Add built-in effects (Console, Fail, State) to run block contexts
- Suppress dead code warnings in diagnostics, modules, parser

Update all example programs with:
- Expected output documented in comments
- Proper run...with statements to execute code

Add new example programs:
- behavioral.lux: pure, idempotent, deterministic, commutative functions
- pipelines.lux: pipe operator demonstrations
- statemachine.lux: ADT-based state machines
- tailcall.lux: tail call optimization examples
- traits.lux: type classes and pattern matching

Add documentation:
- docs/IMPLEMENTATION_PLAN.md: feature roadmap and status
- docs/PERFORMANCE_AND_TRADEOFFS.md: performance analysis

Add benchmarks for performance testing.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/datatypes.lux

@@ -1,4 +1,10 @@
 // Demonstrating algebraic data types and pattern matching
+//
+// Expected output:
+// Tree sum: 8
+// Tree depth: 3
+// Safe divide 10/2: Result: 5
+// Safe divide 10/0: Division by zero!
 
 // Define a binary tree
 type Tree =
@@ -31,7 +37,7 @@ fn depth(tree: Tree): Int =
 // Leaf(1) Leaf(2)
 
 let myTree = Node(Node(Leaf(1), Leaf(2)), Leaf(5))
-let total = sumTree(myTree)
+let treeSum = sumTree(myTree)
 let treeDepth = depth(myTree)
 
 // Option type example
@@ -42,5 +48,15 @@ fn safeDivide(a: Int, b: Int): Option<Int> =
 fn showResult(result: Option<Int>): String =
     match result {
         None => "Division by zero!",
-        Some(n) => "Result: " + n
+        Some(n) => "Result: " + toString(n)
     }
+
+// Print results
+fn printResults(): Unit with {Console} = {
+    Console.print("Tree sum: " + toString(treeSum))
+    Console.print("Tree depth: " + toString(treeDepth))
+    Console.print("Safe divide 10/2: " + showResult(safeDivide(10, 2)))
+    Console.print("Safe divide 10/0: " + showResult(safeDivide(10, 0)))
+}
+
+let output = run printResults() with {}