Cli cleanup

[cs01]

Summary

CLI cleanup: remove musl support, fix Mac issues, unify argument parsing, and fix cross-compilation.

Musl removal

• Remove all musl/Alpine support from target resolution, compiler linking, SDK scripts, and CI
• Remove build-linux-musl CI job (was Alpine-based)
• Remove detect_libc() from installer — was incorrectly detecting musl on Ubuntu
• Simplify LibC type to just "gnu" | "system"

Installer improvements

• Fix platform detection (no longer misidentifies Ubuntu as musl)
• Add export PATH after install so chad is available immediately without opening a new shell

CLI argument parsing

• Migrate chad-node.ts from manual for-loop arg parsing to ArgumentParser (same parser the native binary uses)
• Copy argparse.ts into src/ so tsc can compile it (rootDir restriction prevents importing from lib/)
• Wire up the --verbose flag in the native binary (was declared but never connected to setVerbose)

Cross-compilation

• Restrict --target to linux-x64 for build/run commands (the only supported cross-compile target)
• chad ir can still target any platform since it only emits LLVM IR
• Update help text in both CLI entry points
• Package glibc sysroot in target SDK (CRT objects, system libraries, GCC support files)
• Handle Ubuntu's .a linker scripts that contain absolute paths — resolve referenced archives and rewrite scripts with local filenames
• Force -static when cross-compiling to avoid .so linker script relocation issues
• Add explicit -L<sysroot>/usr/lib to bypass multiarch path detection

Fix chad run on Mac (native binary)

• Root cause: cs_execSync uses popen() which captures stdout into a buffer. When the native chad run called child_process.execSync(cmd), the user program's output was captured and silently discarded
• Fix: add cs_exec_passthrough() in child-process-bridge.c using system() which inherits stdin/stdout/stderr
• Wire it through codegen (calls.ts, llvm-declarations.ts) and use it in chad-native.ts

Fix chad watch on Mac (native binary)

• Root cause: kqueue only watched directories with NOTE_WRITE, but in-place file edits don't trigger NOTE_WRITE on the directory fd (only directory entry changes like create/delete/rename do)
• Fix: watch both directories (for new file creation) AND individual source files (with NOTE_WRITE | NOTE_ATTRIB | NOTE_DELETE | NOTE_RENAME)
• Handle the "write-to-temp-then-rename" editor pattern by detecting NOTE_DELETE/NOTE_RENAME and re-opening stale file descriptors

CI

• Remove build-linux-musl job and all references to it
• Add hello.ts creation step before cross-compile test (file doesn't exist in repo)
• Cherry-pick e2e bridge linking tests: JSON, regex, child_process, hackernews smoke tests in test-artifact job
• Add lib/ artifact verification step

Test plan

• All unit tests pass (329 pass, 1 pre-existing network failure from missing multipart-bridge.o)