Require main function as program entry point

Programs must now define a `main : List String -> a` function as their
entry point. Tail expressions are deprecated and will be ignored with
a warning.

- Add main function detection and signature validation in compile phase
- Generate code to call main with command-line arguments (converted to List)
- Remove IO.args from runtime (args now passed to main directly)
- Prevent optimizer from inlining/removing main function
- Update all examples to use main function instead of tail expressions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: brielov

examples/algorithm-w/main.alg

@@ -424,4 +424,4 @@ let result =
   t1 + t2 + t3 + t4 + t5 + t6 + t7 + t8 + t9 + t10 + t11 + t12 + t13 + t14 + t15
 
 -- Expected: 14 (all pass except omega which should fail occurs check)
-result
+let main = args -> IO.printLine (Int.toString result)

examples/algorithms/main.alg

@@ -213,4 +213,4 @@ let result =
   testTreeAlgorithms                        -- 1345689
                                             -- Total: 1482028
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/basics/main.alg

@@ -311,4 +311,4 @@ let result =
   testIntConversion        -- 177
                            -- Total: 1233
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/data-structures/main.alg

@@ -155,4 +155,4 @@ let testAssoc =
 
 let result = testBST + testStack + testQueue + testAssoc  -- 30
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/data-types/main.alg

@@ -426,4 +426,4 @@ let result =
   testComplexTypes                          -- 44
                                             -- Total: 1151
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/division-safety/main.alg

@@ -51,4 +51,4 @@ let result =
   avg1 + avg2               -- 20 + 0 = 20
   -- Total: 20 + 4 + 20 = 44
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/exhaustiveness-check/main.alg

@@ -75,4 +75,4 @@ let result =
   c1 + c2 + c3 + r1 + r2 + u1 + u2 + b1 + b2 + h1 + h2 + p1 + p2
   -- Expected: 3 + 5 + 4 + 1 + 0 + 42 + 99 + 1 + 0 + 10 + 0 + 6 + 9 = 180
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/functions/main.alg

@@ -311,4 +311,4 @@ let result =
   testLambdas                                -- 101
                                              -- Total: 1754
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/modules/main.alg

@@ -195,4 +195,4 @@ let testCounter =
 
 let result = testMath + testVec2 + testStack + testQueue + testCounter
 
-result
+let main = args -> IO.printLine (Int.toString result)

examples/or-patterns/main.alg

@@ -70,4 +70,4 @@ let result =
   (if startsWithZeroOrOne [5, 2, 3] then 1 else 0)   -- 0
   -- Total: 1 + 0 + 1 + 1 + 0 + 1 + 1 + 42 + 0 + 0 + 1 + 1 + 0 + 1 + 1 + 0 = 51
 
-result
+let main = args -> IO.printLine (Int.toString result)