Engine: crash reports, a log file and bug report drafts (#107)

crash: a panic hook and a locked per-run command journal (adapted from
SolidCraft's crash reports). A panic in a command becomes a report with
the model from before it and the command; one outside commands, or an
unclean exit found at the next start (abort, segfault, a crash in a
graphics driver, a kill: what #248 needs), a report with the model the
journal starts from (autosave, file or a copy) and the commands since,
the last control request and the dead run's log lines. Reports are
bounded, deduplicated by signature and replayable (crash::replay, with
writes confined to a scratch folder). The crash folder follows the
automation temp area in --control and CI runs.

logfile: a small size-rotated file logger behind the log facade.

bug_report: GitHub bug-form drafts. Version, OS and what happened by
default, home folder shown as ~; the command journal only with Share my
session, the model only with Include the model as well; a session too
long for the link becomes a file to attach and the clipboard text.

Commands: diagnostics.crash_reports, diagnostics.crash_report,
diagnostics.bug_report (Tools › Help, with its icon) and
diagnostics.crash_test (FIELDCRAFT_CRASH_TEST=1 only).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/autosave.rs

@@ -47,6 +47,7 @@ impl Autosaver {
         let bytes = s.file_bytes(None)?;
         self.slot.write(&bytes, s.path.as_deref(), s.model.nodes().len(), s.model.elements().len())?;
         self.saved = Some(s.revision());
+        crate::crash::autosaved(s, &self.slot.file());
         Ok(true)
     }