Add site scan, editor-based publishing workflow and subfolder support

Adds a whole-site "Site scan" that analyses pages, images and SEO tags and
makes pages editable in one step, moves Save Draft / Schedule Publish /
Publish Now into the content editor, supports installs in a subfolder, and
hardens metadata handling. Only the cms/ directory is changed.

Added
- Site scan (Tools > Site scan, administrators): reports pages, folders,
  editable/untagged pages, images without alt text, broken local
  references, unused uploads and missing title/description/Open Graph
  tags; then tags <main> or top-level article/section content areas,
  images outside editable regions and photo placeholders, and inserts only
  missing SEO tags. Page source is edited byte-for-byte (no DOM
  re-serialisation), a revision is kept for every changed page, later scans
  list only pages that still need changes, and work runs in small batches
  with a progress bar and "N of M pages" count. New administrator-only
  actions: listSitePages, analyseSitePages, applySiteTagging.
- Click-to-edit images and photo placeholders (role="img" boxes) with a
  Media Library picker and alt text.
- Subfolder installs (basePath / siteRoot auto-detected); root installs
  behave as before.
- Audit/activity entries for cancelled schedules, image uploads, alt-text
  changes and failed scheduled publications (shared Activity class).
- Snackbar (success/error) and table-style dialogs for the page picker,
  revision history, dashboard, shared content, menus and site scan.

Changed
- Editor actions are now Save Draft | Schedule Publish | Publish Now |
  Cancel; saving in the editor and applying image/SEO changes stores a
  private draft. The toolbar no longer has Save Draft, Schedule or Publish.
- CMSController split into PagePaths, ContentDom and Activity; entry points
  share cms/bootstrap.php. Restoring a deleted page uses
  PageNotFoundException instead of matching an error message.

Fixed
- Lost updates on JSON metadata (locked FileStore::update).
- Non-atomic site-wide shared-content/menu writes; non-ASCII text handling.
- Scheduled publishing contending for a lock on every request.
- Revision pruning dropping the newest revision (revisions gain a "ts").
- Stale cached pages in the editor preview after a site is replaced.
- Saved drafts reloading without stylesheets or the correct page path, and
  Publish discarding a draft that was not re-offered in the same session.
- HTML entities in page titles; backslashes in folder names on Windows.

Migration: no manual steps. basePath/siteRoot are optional and detected
automatically. The analyseSite action was replaced by listSitePages and
analyseSitePages.

cms/logs/index.php

@@ -1,4 +1,4 @@
 <?php
 // Audit logs are not a public attraction; return to the authenticated CMS instead.
 http_response_code(404);
-header("Location: /cms/");
+header("Location: ../");