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/cmd/mod.rs

@@ -6,6 +6,7 @@ mod contact;
 pub(crate) mod datum;
 pub(crate) mod deck;
 pub(crate) mod define;
+pub mod diagnostics;
 mod edit;
 pub(crate) mod file;
 pub(crate) mod forms;
@@ -153,6 +154,10 @@ pub static ALL: &[CommandSpec] = &[
     results::FRAME,
     results::REACTIONS,
     results::CLEAR,
+    diagnostics::CRASH_REPORTS,
+    diagnostics::CRASH_REPORT,
+    diagnostics::BUG_REPORT,
+    diagnostics::CRASH_TEST,
 ];
 
 /// The problem with required parameter `key`: [`ProblemKind::Required`] when it is left out,