docs: add project explanation and handoff guide

.project-docs/30-worklog/current-state.md

@@ -19,6 +19,17 @@ preserves its no-formula contract. Both publishers upload new workbook and `resu
 immutable OSS adapter, while download routing retains controlled-local compatibility for historical records and keeps
 `.web-jobs` queue state local.
 
+## Documentation And Repository Handoff On 2026-09-06
+
+- Added root `PROJECT_GUIDE.md` as a Chinese project explanation and handoff guide. It consolidates the project goal,
+  architecture, XML/manual-review/monthly/Booking/company-report/BI flows, module map, configuration, local startup,
+  migrations, tests, deployment, troubleshooting, security boundaries and new-member checklist. The root README links
+  to it as the complete project entry point.
+- The guide explicitly separates repository implementation from production deployment and business acceptance, and
+  routes changing operational gaps back to `90-maintenance/stale-items.md`. Local Markdown links, Git whitespace and
+  the documented Web/worker CLI entry points pass. This documentation-only task changed no application behavior,
+  database, object store, runtime process or business data.
+
 ## Daily Interaction Correction On 2026-08-11
 
 - The local source now treats Daily Report rows as informational table rows rather than hidden log controls. It removes