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

docs/features.md

@@ -6,7 +6,7 @@ Every entry is a toolbar button. **Ready** entries run their command; **coming s
 shown greyed with the roadmap milestone that brings them (ROADMAP.md). Scripts, the command line,
 the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 
-65 ready, 41 coming soon.
+66 ready, 41 coming soon.
 
 ## Geometry
 
@@ -163,3 +163,4 @@ the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 | View | Show All — Show every item hidden in the viewport (hide, show and isolate items from the browser) | ready | `view.show_all`, (`view.hide`), (`view.show`), (`view.isolate`) |
 | History | Undo — Undo the last command that changed the model | ready | `edit.undo` |
 | History | Redo — Redo the command undone last | ready | `edit.redo` |
+| Help | Report a Bug — Draft a GitHub bug report with the version, the OS and the last error; you review it, and nothing is sent until you submit it | ready | `diagnostics.bug_report`, `diagnostics.crash_reports`, `diagnostics.crash_report`, `diagnostics.crash_test` |