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/README.md

@@ -0,0 +1,28 @@
+# Documentation
+
+## For users
+
+| Page | What it covers |
+|---|---|
+| [Installation](INSTALL.md) | Packages, building from source, first sign-in, updating and uninstalling |
+| [User guide](USER_GUIDE.md) | My files, available offline, synced folders, conflicts, Photos, sharing, Trash and versions, Computers, the search launcher, the tray |
+| [Command-line reference](CLI.md) | Every `pdfs` command, grouped by task, and scripting with `--json` |
+| [Configuration](CONFIGURATION.md) | `config.json`, environment variables, file locations, the systemd service |
+| [Troubleshooting](TROUBLESHOOTING.md) | Diagnosing problems, common symptoms, starting over, reporting a bug |
+| [Recovering on a new computer](RECOVERY.md) | What survives a lost machine and how to restore your synced folders |
+| [Changelog](CHANGELOG.md) | What changed in each release |
+
+## For contributors
+
+| Page | What it covers |
+|---|---|
+| [Development guide](DEVELOPMENT.md) | Building, running and debugging from source; releasing |
+| [Architecture](ARCHITECTURE.md) | Crates, read and write paths, sync engine, control protocol, threads, threat model |
+| [Testing](TESTING.md) | Unit tests and the FUSE acceptance suite |
+| [Translating](TRANSLATING.md) | Adding and updating translations |
+| [Roadmap](ROADMAP.md) | Planned work and verification still owed |
+| [Bug ledger](BUGS.md) | Every tracked defect with its analysis and status |
+| [UI/UX plan](UI_UX_PLAN.md) | Design audit and notes behind the 2.x desktop app |
+
+Also see [CONTRIBUTING.md](../CONTRIBUTING.md) and [SECURITY.md](../SECURITY.md) in the repository
+root.