docs: publish docs/ to the GitHub wiki and reorganise the user guide

- scripts/publish-wiki.sh publishes every page listed in SECTIONS, copies
  images, writes a sectioned sidebar and footer, and removes stale pages.
  --check fails on links to missing files or headings and on docs pages
  that are neither published nor excluded.
- New wiki.yml runs the check on pull requests and pushes to main, and
  publishes when release.yml calls it or when started by hand.
- Split USER_GUIDE.md into topic pages (files, synced folders, photos,
  sharing, computers, launcher and tray); add Getting started and FAQ.
- Make the COPR repository the main Fedora path, with update and
  uninstall steps for every package type.
- Fix the stale CAPTCHA note in CLI.md, document pdfs unlock and lock,
  and drop the broken AGENTS.md link from CONTRIBUTING.md.

docs/README.md

@@ -1,19 +1,48 @@
-# Documentation
+# Proton Drive for Linux documentation
 
-## For users
+Proton Drive for Linux is an unofficial Proton Drive client for the Linux desktop. Your Drive
+appears as a folder that downloads files when you open them, local folders are backed up and kept
+in sync, and a GTK app with a tray icon and a search launcher covers Photos, sharing and more. A
+command-line client does all of it from a terminal.
+
+These pages are also published as the
+[wiki](https://github.com/narrrl/proton-drive-linux/wiki), generated from the
+[`docs/`](https://github.com/narrrl/proton-drive-linux/tree/main/docs) folder of the repository.
+
+## Where to start
+
+- **New here?** [Getting started](GETTING_STARTED.md) takes you from installing to your first
+  synced folder.
+- **Installing or updating?** [Installation](INSTALL.md) covers Fedora (COPR), Arch (AUR),
+  Debian and Ubuntu, NixOS, and building from source.
+- **Something not working?** [Troubleshooting](TROUBLESHOOTING.md) starts with `pdfs diagnose`
+  and goes through common problems.
+- **New computer, or the old one is gone?** [Recovering on a new computer](RECOVERY.md) gets your
+  synced folders back.
+- **Quick question?** Try the [FAQ](FAQ.md).
+
+## Using it
+
+| Page | What it covers |
+|---|---|
+| [User guide](USER_GUIDE.md) | How the pieces fit together, the words the app uses, preferences |
+| [Files and offline access](FILES.md) | The `~/ProtonDrive` folder, keeping files available offline, the Trash, earlier versions |
+| [Synced folders](SYNCED_FOLDERS.md) | Backing up local folders, excluding files, changes waiting to upload, conflicts, pausing |
+| [Photos](PHOTOS.md) | Timeline, albums, places, duplicates, importing from Google Photos |
+| [Sharing](SHARING.md) | Invitations, public links, items shared with you |
+| [Computers](COMPUTERS.md) | Other computers in your account, syncing several computers |
+| [Search launcher and tray](LAUNCHER_AND_TRAY.md) | Finding files from a keyboard shortcut, the tray icon |
+
+## Reference
 
 | 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, sync issues and 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 |
 | [Security model](SECURITY_MODEL.md) | What protects your files, what is kept on this computer, what the client connects to |
 | [Changelog](CHANGELOG.md) | What changed in each release |
 
-## For contributors
+## Contributing
 
 | Page | What it covers |
 |---|---|
@@ -24,5 +53,5 @@
 | [Roadmap](ROADMAP.md) | Planned work and verification still owed |
 | [Bug ledger](BUGS.md) | Every tracked defect with its analysis and status |
 
-Also see [CONTRIBUTING.md](../CONTRIBUTING.md) and [SECURITY.md](../SECURITY.md) in the repository
-root.
+Also see [CONTRIBUTING.md](../CONTRIBUTING.md), and [SECURITY.md](../SECURITY.md) to report a
+vulnerability privately.