Enhance timeline editor left sidebar with collapsible content summary

- Add comprehensive linked content summary section with collapsible content type groups
- Replace basic Timeline Stats with detailed content breakdown showing counts and items
- Remove Import Events button to streamline Quick Actions
- Implement Alpine.js methods for managing collapsible sections
- Show up to 10 items per content type with "X more" indicators
- Add Timeline Stats section below content summary with event count, word count, and total linked pages
- Links open in new tabs for easy navigation
- Maintain clean, organized left sidebar layout with consistent styling

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/controllers/timelines_controller.rb

@@ -79,6 +79,7 @@ class TimelinesController < ApplicationController
     
     # Get content already linked to other events in this timeline
     @timeline_linked_content = {}
+    @timeline_content_summary = {}
     timeline_entity_ids = @timeline.timeline_events
                                    .joins(:timeline_event_entities)
                                    .pluck('timeline_event_entities.entity_type', 'timeline_event_entities.entity_id')
@@ -89,9 +90,22 @@ class TimelinesController < ApplicationController
       content_class = content_class_from_name(entity_type)
       next unless content_class
       
+      # Original data for link modal
       @timeline_linked_content[entity_type] = content_class.where(id: entity_ids)
                                                           .where(user: current_user)
                                                           .limit(20)
+      
+      # Enhanced data for content summary sidebar
+      all_content = content_class.where(id: entity_ids)
+                                .where(user: current_user)
+                                .order(:name)
+      
+      @timeline_content_summary[entity_type] = {
+        count: all_content.count,
+        items: all_content.limit(10), # Show first 10, with expansion option
+        total_items: all_content.count,
+        content_class: content_class
+      }
     end
   end