Log like a debug build on macOS, where a Mac user can find it

Nobody working on DarkRoom has a Mac, so every macOS build is in the hands
of someone who can send a log and cannot attach a debugger. Three changes
make that log worth sending:

- The desktop's default filter on macOS is `debug` for every `dr_*` crate,
  the desktop crate and `onnxruntime` (the runtime's own session log).
- The state directory — the log and crash records — is `~/Library/Logs`
  on macOS rather than the `~/.local/state` Finder hides; Console.app
  lists it. Config and data keep the Unix rules.
- A `diagnostic` cargo profile: release plus line tables, so a crash
  record's backtrace reads file:line. On macOS the tables are in the
  `.dSYM` beside the executable, which the bundle must keep.

platform/dr-plat/src/crash.rs

@@ -98,7 +98,8 @@ pub fn set_state_dir(dir: PathBuf) {
 
 /// Where this application keeps state that is neither configuration nor cache.
 ///
-/// `$XDG_STATE_HOME/darkroom`, falling back to `~/.local/state/darkroom`.
+/// `$XDG_STATE_HOME/darkroom`, falling back to `~/.local/state/darkroom` —
+/// `~/Library/Logs/darkroom` on macOS (`dirs`).
 /// State rather than cache because a crash record must survive the sweep that
 /// a cache directory exists to permit, and rather than config because it is
 /// not something the user edits.