feat: reworked the category editing

specs/editor_settings.allium

@@ -14,7 +14,6 @@ value SettingsView {
     active_sections: List<String>       -- visible sections after search filter
     project_section: SettingsProjectSection?
     editor_section: SettingsEditorSection?
-    categories: List<SettingsCategoryRow>
     ai_section: SettingsAISection?
     technology_section: SettingsTechnologySection?
     publishing_section: SettingsPublishingSection?
@@ -42,16 +41,6 @@ value SettingsEditorSection {
     hide_unchanged_regions: Boolean     -- checkbox
 }
 
-value SettingsCategoryRow {
-    name: String                        -- read-only for protected categories
-    title: String                       -- editable
-    render_in_lists: Boolean            -- checkbox
-    show_titles: Boolean                -- checkbox
-    post_template_slug: String?         -- select
-    list_template_slug: String?         -- select
-    is_protected: Boolean               -- true for: article, aside, page, picture
-}
-
 value SettingsAISection {
     online: SettingsAIEndpoint
     airplane: SettingsAIEndpoint
@@ -97,11 +86,6 @@ value SettingsDataSection {
     rebuild_targets: List<String>       -- posts | media | scripts | templates | links | thumbnails | embedding
 }
 
-invariant SettingsProtectedCategories {
-    -- Protected categories (article, aside, page, picture) cannot be deleted.
-    -- Their Remove button is disabled.
-}
-
 invariant SettingsMCPAgents {
     -- MCP section has exactly 7 agent rows in this order:
     -- Claude Code, Claude Desktop, GitHub Copilot, Gemini CLI,