docs: update documentation to match current implementation

- SKILLS.md: Update roadmap phases with actual completion status
  - Phase 0-1 complete, Phase 2-5 partial, resolved design decisions
- OVERVIEW.md: Add HttpServer, Test effect, JIT to completed features
- ROADMAP.md: Add HttpServer, Process, Test effects to done list
- VISION.md: Update Phase 2-3 tables with current status
- guide/05-effects.md: Add Time, HttpServer, Test to effects table
- guide/09-stdlib.md: Add HttpServer, Time, Test effect docs
- reference/syntax.md: Fix interpolation syntax, remove unsupported literals
- testing.md: Add native Test effect documentation

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

docs/testing.md

@@ -2,6 +2,50 @@
 
 This guide explains how to write and run tests for Lux programs.
 
+## Native Test Effect
+
+Lux provides a built-in `Test` effect for writing tests:
+
+```lux
+fn runTests(): Unit with {Test, Console} = {
+    // Basic assertions
+    Test.assert(1 + 1 == 2, "basic math")
+
+    // Equality checks
+    Test.assertEqual(List.length([1, 2, 3]), 3, "list length")
+
+    // Boolean assertions
+    Test.assertTrue(String.contains("hello", "ell"), "contains check")
+    Test.assertFalse(List.isEmpty([1]), "non-empty list")
+}
+
+// Run with the test handler
+fn main(): Unit with {Console} = {
+    run runTests() with { Test = testReporter }
+}
+
+let result = run main() with {}
+```
+
+### Test Effect Operations
+
+| Operation | Purpose |
+|-----------|---------|
+| `Test.assert(condition, message)` | Assert condition is true |
+| `Test.assertEqual(expected, actual, message)` | Assert values are equal |
+| `Test.assertTrue(condition, message)` | Assert condition is true (alias) |
+| `Test.assertFalse(condition, message)` | Assert condition is false |
+
+### Running Tests
+
+```bash
+# Run a test file
+lux tests/my_tests.lux
+
+# Run with the test runner
+lux test tests/
+```
+
 ## Test File Structure
 
 Lux uses a simple test framework based on comparing program output against expected results. Tests are organized in the `tests/` directory.