feat(17-01): richeditor field type on the seaglass sanitizer

- seaglass (new module): bluemonday v1.0.27 policy ported from Journal
  without the Blog Editor rules, byte-stable token comparison,
  SanitizeReport, Sanitize, Check, Removals
- cabana: type richeditor (common keys plus size); every create and update
  value sanitized before Fill, non-string values are a 422, removals become
  meta.notices; settings and relation forms refuse the type
- backend lang richeditor.removed_* and markup_changed (en, pl plurals)
- TestSeaglassSmoke, TestCompanionsRichEditorSmoke, README and docs

README.md

@@ -108,6 +108,7 @@ The `migrate`, `migrate:status`, `migrate:rollback`, `serve` and admin commands
 | [party](modules/party/README.md) | Compiled plugin registry that orders plugins by their dependencies and runs their Register and Boot lifecycle. | The guest list and the order people arrive in; it registers plugins and boots them in dependency order. |
 | [phrasebook](modules/phrasebook/README.md) | Namespaced translation catalogs loaded from plugin YAML, with locale fallback, placeholder interpolation and CLDR pluralization. | What you pack to speak the local language on holiday; it holds the translations. |
 | [postcard](modules/postcard/README.md) | Transactional mail from plugin-owned Markdown templates and layouts, delivered through a memory, log or SMTP driver. | What you send home in summer; it delivers the application's mail. |
+| [seaglass](modules/seaglass/README.md) | HTML sanitizer for stored rich text: a bluemonday allowlist policy that returns clean HTML byte for byte and reports what it removed from the rest. | Glass the sea has worn smooth; rough HTML goes in and only the safe, smooth part comes out. |
 | [sieve](modules/sieve/README.md) | Generic, dependency-free collection helpers that the standard library slices and maps packages lack: mapping, filtering, reducing, keying, grouping, deduplicating, partitioning and finding, plus a small set type. | A sand sieve: you shake a collection through it and keep what you need; map, filter and reduce for slices and maps. |
 | [signpost](modules/signpost/README.md) | Menu item type registry that collects the typed menu item types plugins register at boot, layers their URL patterns with host overrides and resolves menu and sitemap items through the owning plugin. | A beach signpost points the way to places; the registry tells menus and sitemaps where each item leads. |
 | [sunrise](modules/sunrise/README.md) | Bootstrap script that installs the summer CLI and creates a new SummerCMS application, or updates an existing one, in one command, embedded so it is versioned with the framework. | The start of a summer day; it starts a new application, or updates one, in one command. |