feat(crash): Breakpad-style minidumps on macOS and Windows

Ghostty links sentry-native with the breakpad backend on every platform
(SharedDeps.zig), so it writes minidumps on macOS and Windows as well.
- macOS: a Mach exception port handler thread (structured like
  Breakpad's exception_handler) catches EXC_BAD_ACCESS/BAD_INSTRUCTION/
  ARITHMETIC/BREAKPOINT, suspends other threads, reads the crashed
  thread state and writes a minidump via minidump-writer as the
  event.minidump attachment, then restores the previous ports so the
  BSD signal and default termination follow. The signal path remains
  the fallback (and handles SIGABRT); a watchdog alarm bounds dumping.
- Windows: SetUnhandledExceptionFilter hands off to a pre-started dump
  thread using minidump-writer's dump_crash_context.
- The screen-file open action decodes the escaped path to raw OS bytes
  (also for the C action passed to embedders).

macOS/Windows code is compile-checked (clippy -D warnings) only; the
shared Mach message decoding and minidump attachment logic have Linux
unit tests. Platform matrix in docs/rewrite/notes/crash-CR.md.

Test Plan:
- cargo test --workspace (3348 passed)
- just check-macos; just check-macos x86_64-apple-darwin; just check-windows

crates/ghostty-crash/Cargo.toml

@@ -22,9 +22,18 @@ libc = "0.2"
 [target.'cfg(target_vendor = "apple")'.dependencies]
 mach2 = "0.6"
 
-[target.'cfg(target_os = "linux")'.dependencies]
+[target.'cfg(any(target_os = "linux", target_os = "macos", windows))'.dependencies]
 minidump-writer = "0.13.0"
 
+[target.'cfg(windows)'.dependencies]
+windows-sys = { version = "0.61", features = [
+  "Win32_Foundation",
+  "Win32_Security",
+  "Win32_System_Diagnostics_Debug",
+  "Win32_System_Kernel",
+  "Win32_System_Threading",
+] }
+
 [dev-dependencies]
 minidump = "0.27.0"
 tempfile = "3.27.0"