Add syndication and database source editor extensions.

This commit adds two production extensions to composer.json:

- se7enxweb/syndication ~1.2.0 — enables SOAP-based content syndication
  between separate Exponential installations, supporting centralized user
  registration, content syncing, feed sources, import/export filters and
  cronjob-driven replication for multi-site deployments.

- se7enxweb/sevenx_dse ~1.0.0 — embeds AdminNeo as a permission-gated
  database source editor within the admin UI, providing raw SQL execution,
  table browsing, import/export and multi-driver support (MySQL, PostgreSQL,
  SQLite, MS SQL, Oracle) without leaving Exponential.

Both packages are installed through the existing se7enxweb/exponential-legacy-installer
and are managed alongside the other eZ Publish Legacy extensions in composer.json.

Add ICONS.md documentation for the mainlined icon theme support.

Documents the bciconextensions and bciconextensions_share_icons
integration into Exponential 6.0.15-alpha so developers can:

- Place icon themes in extension/<name>/icons/<theme>/ instead of patching
  the kernel or copying files into share/icons.
- Configure theme fallback chains: current theme → AdditionalThemeList[]
  themes → StandardTheme.
- Configure repository fallback chains: extension icon directories are
  searched before the default share/icons repository.
- Add custom class, MIME, class group, action, and flag icons through
  icon.ini settings and theme icon.ini maps.
- Remove the legacy bciconextensions and bciconextensions_share_icons
  extensions from ActiveExtensions[] after upgrading.
- Test the icon operators in 2 minutes using the shipped job icon and a
  command-line template snippet.

The documentation also covers web server requirements for serving static
icons from extension directories and includes a complete INI reference.

Mainline bciconextensions icon theme support and ship a default job icon.

This integrates the legacy bciconextensions and bciconextensions_share_icons
functionality into the Exponential kernel so sites no longer need a kernel
override or special autoload configuration to use extension-resident icon
themes.

Features and developer benefits:

* Extension-resident icon themes — place icon sets in
  extension/<name>/icons/<theme>/ instead of copying files into share/icons or
  patching the kernel. This keeps custom icon assets with the extension that
  ships them and simplifies updates.

* Theme fallback chain — the icon engine searches the current theme first,
  then any AdditionalThemeList[] themes, and finally the StandardTheme. This
  makes it safe to layer admin or custom themes on top of a base theme.

* Repository fallback chain — for each theme, extension icon directories are
  searched before the default share/icons repository. Sites can override a
  stock icon by shipping a same-named icon in an extension without touching
  core files.

* Default icon fallback — when an icon cannot be resolved, the theme or
  override Default icon is used instead of generating a broken <img> tag,
  which keeps the admin interface and front-end templates visually stable.

* Static file serving — icons under extension/*/icons/ are ordinary static
  files served directly by the web server, so no extra PHP work is done for
  each image request.

* Default job icon shipped — the job.png icon from bciconextensions_share_icons
  is now part of the crystal-admin theme and mapped to the job class by
  default.

Files changed:

* kernel/common/ezwordtoimageoperator.php — extension/theme search, fallback
  handling, and IconExtensions[] support.
* settings/icon.ini — added StandardTheme, AdditionalThemeList[], and
  IconExtensions[] defaults.
* share/icons/crystal-admin/icon.ini — added ClassMap[job]=apps/job.png.
* share/icons/crystal-admin/16x16_indexed/apps/job.png and
  share/icons/crystal-admin/32x32/apps/job.png — new default icon assets.

Add sevenx_valkey_cache to composer suggest metadata.

This exposes the Valkey-backed cache extension to users running
`composer install` or browsing the package suggestions. Sites that install
the extension benefit from faster content view, INI, and template-block
caching by moving cache traffic from the local filesystem to a shared
Redis/Valkey backend, which reduces disk I/O, lowers cache-directory lock
contention, and makes multi-node horizontal scaling simpler.

Make the Valkey view-cache hook optional for sites without the extension.

This keeps the Exponential kernel safe to deploy on sites that do not
have the sevenx_valkey_cache extension installed or autoloaded. When the
sevenxValkeyCacheBlock class is present the kernel uses the fast Redis/
Valkey-backed view cache; when it is not present the kernel falls back to
the standard eZClusterFileHandler file-based view cache. This prevents a
fatal "class not found" error on content views and removes the hard
dependency between the patched kernel and the extension class files.

Developers can now:
- Upgrade to the Valkey-aware kernel without being forced to install the
  extension.
- Ship a single kernel build to both Valkey-enabled and non-Valkey sites.
- Enable Valkey caching later simply by installing the extension and
  regenerating autoloads.

Add Redis/Valkey kernel hooks for content view and compiled INI caches

Add extension suggestions to composer.json

Adds owsimpleoperator, adminaid, ezpm, hcaptcha and syndication

to the suggest list with detailed feature descriptions.