docs: restructure and update documentation for 2.5.0

Split the README into a short front page and task-oriented pages under
docs/: installation, user guide, CLI reference, configuration and
troubleshooting, with an index in docs/README.md. Rewrite RECOVERY.md
around Continue This Backup Here and Restore Folders, and DEVELOPMENT.md
around running, debugging and releasing from source.

Bring ARCHITECTURE.md up to date with the read path, push events, the
thread map, conflict copies and the machine profile, and move the feature
design notes there. Collect planned work in ROADMAP.md. Link the threat
model from SECURITY.md and the translation rules from CONTRIBUTING.md.

Add scripts/publish-wiki.sh, which mirrors the user pages to the GitHub
wiki with rewritten links and only pushes with --push.

docs/TESTING.md

@@ -78,10 +78,9 @@ in-flight `.crdownload` must not be sealed as a revision) and B74 (a file
 renamed after close must keep its content) need a real mount and a reachable
 daemon; they are skipped, not failed, without one.
 
-B74 is currently **failing** — it is a live data-loss defect, not a regression
-guard, and it was found by exactly this mechanism: the B70 case failed, and
-narrowing it produced a smaller reproduction that has its own case now. Expect a
-red run against a real mount until it is fixed.
+B74 was found by exactly this mechanism: the B70 case failed, and narrowing it
+produced a smaller reproduction that got its own case. The defect is fixed and
+live-validated (2026-07-26); the case now guards against its return.
 
 **B79** (an on-demand device folder accepts writes) discovers its target from
 `pdfs locations --json` and skips when this machine has no mounted on-demand