feat: restructure repo, borrow checker, expanded stdlib

- Reorganize repository to Rust-style layout:
  compiler/bootstrap/  compiler/selfhost/  compiler/tests/
  library/std/  library/runtime/  tests/  tools/
- Add buxs/ Windows-compatible project root
- Add borrow checker tests and implement:
  - Alias analysis (double mutable borrow detection)
  - Use-after-move detection for own T
- Expand standard library:
  - Std::Os: Args, Env, Cwd, Chdir
  - Std::Time: NowMs, NowUs, SleepMs
  - Std::Process: Run, Output
  - Std::Io: PrintInt64 (fixes 32-bit truncation bug)
- Add examples: os_time.bux, process.bux
- Fix PrintInt to use int64_t in C runtime

compiler/selfhost/main.bux

@@ -0,0 +1,23 @@
+// main.bux — Entry point for the Bux self-hosting compiler
+module Main {
+
+// C runtime for command-line args
+extern func bux_argc() -> int;
+extern func bux_argv(index: int) -> String;
+extern func bux_alloc(size: uint) -> *void;
+
+// Forward declaration from Cli module
+func Cli_Run(args: *String, argCount: int) -> int;
+
+func Main() -> int {
+    let count: int = bux_argc();
+    // Allocate array of String pointers
+    let args: *String = bux_alloc(count as uint * 8) as *String;
+    var i: int = 0;
+    while i < count {
+        args[i] = bux_argv(i);
+        i = i + 1;
+    }
+    return Cli_Run(args, count);
+}
+}