refactor(editor): optimize extension register and effects (#10406)

Key Changes:

1. **Code Reorganization and Consolidation**
   - Created new centralized extension management through new files:
     - `enableEditorExtension` in `extensions/entry/enable-editor.ts`
     - `enablePreviewExtension` in `extensions/entry/enable-preview.ts`
   - Removed several spec-related files that are now consolidated:
     - Removed `specs/edgeless.ts`
     - Removed `specs/page.ts`
     - Removed `specs/preview.ts`

2. **Template Management**
   - Added new `register-templates.ts` file to handle template registration
   - Moved template registration logic from `specs/edgeless.ts` to this new file
   - Templates now include both edgeless and sticker templates

3. **Extension Management Changes**
   - Simplified extension enabling process through new centralized functions
   - `enableEditorExtension` now handles both page and edgeless modes
   - `enablePreviewExtension` consolidates preview-related extensions
   - Removed duplicate code for extension management

4. **Preview Functionality Updates**
   - Streamlined preview spec management
   - Consolidated footnote configuration
   - Improved theme and preview extension handling

5. **Dependencies and Effects**
   - Updated how effects are registered and managed
   - Simplified initialization process in `index.ts`
   - More organized approach to handling framework providers

The main theme of this PR appears to be code consolidation and simplification, moving from multiple specialized files to more centralized, reusable extension management. This should make the codebase more maintainable and reduce duplication while keeping the same functionality.

The changes primarily affect the editor's extension system, preview functionality, and template management, making these systems more modular and easier to maintain.

.github/CODEOWNERS

@@ -1 +1,2 @@
 /blocksuite/ @toeverything/blocksuite-core
+/packages/frontend/core/src/blocksuite @toeverything/blocksuite-core