feat: add module import examples and standard library

Module system was already implemented - this adds examples and stdlib:

examples/modules/:
- math_utils.lux: Reusable math functions (square, cube, factorial)
- string_utils.lux: String utilities (repeat, exclaim, greet)
- main.lux: Basic module import example
- main_selective.lux: Selective imports {fn1, fn2}
- main_wildcard.lux: Wildcard imports (module.*)
- use_stdlib.lux: Using the standard library

std/:
- prelude.lux: Core utilities (identity, compose, flip, not, and, or)
- io.lux: I/O helpers (println, readLine, debug)
- option.lux: Option utilities (some, none, map, flatMap, filter)
- result.lux: Result utilities (ok, err, mapOk, mapErr)

Import syntax supports:
- import path/to/module       (access as module.fn)
- import path/to/module as x  (access as x.fn)
- import path/to/module.{a,b} (access as a, b directly)
- import path/to/module.*     (all exports directly)

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

examples/modules/main.lux

@@ -0,0 +1,20 @@
+// Main program that imports modules
+import examples/modules/math_utils
+import examples/modules/string_utils
+
+fn main(): Unit with {Console} = {
+    Console.print("=== Testing Module Imports ===")
+
+    // Use math_utils
+    Console.print("square(5) = " + toString(math_utils.square(5)))
+    Console.print("cube(3) = " + toString(math_utils.cube(3)))
+    Console.print("factorial(6) = " + toString(math_utils.factorial(6)))
+    Console.print("sumRange(1, 10) = " + toString(math_utils.sumRange(1, 10)))
+
+    // Use string_utils
+    Console.print(string_utils.greet("World"))
+    Console.print(string_utils.exclaim("Modules work"))
+    Console.print("repeat(\"ab\", 3) = " + string_utils.repeat("ab", 3))
+}
+
+let output = run main() with {}

examples/modules/main_selective.lux

@@ -0,0 +1,17 @@
+// Test selective imports
+import examples/modules/math_utils.{square, factorial}
+import examples/modules/string_utils as str
+
+fn main(): Unit with {Console} = {
+    Console.print("=== Selective & Aliased Imports ===")
+
+    // Direct imports (no module prefix)
+    Console.print("square(7) = " + toString(square(7)))
+    Console.print("factorial(5) = " + toString(factorial(5)))
+
+    // Aliased import
+    Console.print(str.greet("Lux"))
+    Console.print(str.exclaim("Aliased imports work"))
+}
+
+let output = run main() with {}

examples/modules/main_wildcard.lux

@@ -0,0 +1,14 @@
+// Test wildcard imports
+import examples/modules/math_utils.*
+
+fn main(): Unit with {Console} = {
+    Console.print("=== Wildcard Imports ===")
+
+    // All functions available directly
+    Console.print("square(4) = " + toString(square(4)))
+    Console.print("cube(4) = " + toString(cube(4)))
+    Console.print("factorial(4) = " + toString(factorial(4)))
+    Console.print("sumRange(1, 4) = " + toString(sumRange(1, 4)))
+}
+
+let output = run main() with {}

examples/modules/math_utils.lux

@@ -0,0 +1,14 @@
+// Math utilities module
+// Exports: square, cube, factorial
+
+pub fn square(n: Int): Int = n * n
+
+pub fn cube(n: Int): Int = n * n * n
+
+pub fn factorial(n: Int): Int =
+    if n <= 1 then 1
+    else n * factorial(n - 1)
+
+pub fn sumRange(start: Int, end: Int): Int =
+    if start > end then 0
+    else start + sumRange(start + 1, end)

examples/modules/string_utils.lux

@@ -0,0 +1,11 @@
+// String utilities module
+// Exports: repeat, exclaim
+
+pub fn repeat(s: String, n: Int): String =
+    if n <= 0 then ""
+    else s + repeat(s, n - 1)
+
+pub fn exclaim(s: String): String = s + "!"
+
+pub fn greet(name: String): String =
+    "Hello, " + name + "!"

examples/modules/use_stdlib.lux

@@ -0,0 +1,23 @@
+// Example using the standard library
+import std/prelude.*
+import std/option as opt
+
+fn main(): Unit with {Console} = {
+    Console.print("=== Using Standard Library ===")
+
+    // Prelude functions
+    Console.print("identity(42) = " + toString(identity(42)))
+    Console.print("not(true) = " + toString(not(true)))
+    Console.print("and(true, false) = " + toString(and(true, false)))
+    Console.print("or(true, false) = " + toString(or(true, false)))
+
+    // Option utilities
+    let x = opt.some(10)
+    let y = opt.none()
+    Console.print("isSome(Some(10)) = " + toString(opt.isSome(x)))
+    Console.print("isNone(None) = " + toString(opt.isNone(y)))
+    Console.print("unwrapOr(Some(10), 0) = " + toString(opt.unwrapOr(x, 0)))
+    Console.print("unwrapOr(None, 0) = " + toString(opt.unwrapOr(y, 0)))
+}
+
+let output = run main() with {}