Major Refactor: Infinite Nesting and Enhanced Management UX

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🚀 Major Refactor: Infinite Nesting and Enhanced Management UX

This PR introduces a significant architectural upgrade to cs_dynamicpages, enabling recursive row structures and providing a modern management interface.

🏗️ Architecture & Core Features

• Infinite Nesting: DynamicPageRow is now folderish, allowing rows to contain other rows (e.g., Sliders with Image slides, Accordions with Text blocks, nested Grids).
• Structural Governance: Added registry-driven constraints (top_level_row_types and allowed_child_row_types) to control precisely where specific row types can be added.
• Navigator Sidebar: Introduced a recursive Offcanvas tree UI for high-level management of complex page structures (reordering, adding, editing, or deleting nested items without cluttering the main preview).
• Content Type Consolidation: Merged all row variants into a single, behavior-rich DynamicPageRow content type, with an automatic migration (v2000) for legacy DynamicPageRowFeatured items.

🛠️ UX & Compatibility Improvements

• Control Panel Optimization: Overhauled the configuration interface to use Checkboxes and TextAreas, resolving a known JavaScript indexing bug in z3cform.datagridfield that hid selected items.
• Plone 6.0 Support: Implemented conditional imports for widgets to maintain compatibility with the older plone.app.z3cform versions found in Plone 6.0.
• Context-Aware Vocabulary: The RowType vocabulary now intelligently detects its environment to enforce constraints during content editing while remaining permissive during registry configuration.

📚 Documentation & Maintenance

• Updated Guides: New documentation for 'Structural Governance' and updated registry.xml examples for developers.
• Unified Changelog: Consolidated all news fragments into a single feature entry.
• Verified Stability: All 236 tests passed locally, and codebase maintainability scored 10/10 on Pyroma.

This refactor provides the foundation for building highly complex, structured layouts in Plone Classic UI while keeping the editing experience clean and manageable.