Sets up calendar package with core infrastructure

Adds core calendar package components including:
- Base services for events, resources, and settings
- Calendar app and orchestrator
- Build and bundling configuration
- IndexedDB storage setup

Prepares foundational architecture for calendar functionality

packages/calendar/src/core/BaseGroupingRenderer.ts

@@ -0,0 +1,91 @@
+import { IRenderer, IRenderContext } from './IGroupingRenderer';
+
+/**
+ * Entity must have id
+ */
+export interface IGroupingEntity {
+  id: string;
+}
+
+/**
+ * Configuration for a grouping renderer
+ */
+export interface IGroupingRendererConfig {
+  elementTag: string;      // e.g., 'swp-team-header'
+  idAttribute: string;     // e.g., 'teamId' -> data-team-id
+  colspanVar: string;      // e.g., '--team-cols'
+}
+
+/**
+ * Abstract base class for grouping renderers
+ *
+ * Handles:
+ * - Fetching entities by IDs
+ * - Calculating colspan from parentChildMap
+ * - Creating header elements
+ * - Appending to container
+ *
+ * Subclasses override:
+ * - renderHeader() for custom content
+ * - getDisplayName() for entity display text
+ */
+export abstract class BaseGroupingRenderer<T extends IGroupingEntity> implements IRenderer {
+  abstract readonly type: string;
+  protected abstract readonly config: IGroupingRendererConfig;
+
+  /**
+   * Fetch entities from service
+   */
+  protected abstract getEntities(ids: string[]): Promise<T[]>;
+
+  /**
+   * Get display name for entity
+   */
+  protected abstract getDisplayName(entity: T): string;
+
+  /**
+   * Main render method - handles common logic
+   */
+  async render(context: IRenderContext): Promise<void> {
+    const allowedIds = context.filter[this.type] || [];
+    if (allowedIds.length === 0) return;
+
+    const entities = await this.getEntities(allowedIds);
+    const dateCount = context.filter['date']?.length || 1;
+    const childIds = context.childType ? context.filter[context.childType] || [] : [];
+
+    for (const entity of entities) {
+      const entityChildIds = context.parentChildMap?.[entity.id] || [];
+      const childCount = entityChildIds.filter(id => childIds.includes(id)).length;
+      const colspan = childCount * dateCount;
+
+      const header = document.createElement(this.config.elementTag);
+      header.dataset[this.config.idAttribute] = entity.id;
+      header.style.setProperty(this.config.colspanVar, String(colspan));
+
+      // Allow subclass to customize header content
+      this.renderHeader(entity, header, context);
+
+      context.headerContainer.appendChild(header);
+    }
+  }
+
+  /**
+   * Override this method for custom header rendering
+   * Default: just sets textContent to display name
+   */
+  protected renderHeader(entity: T, header: HTMLElement, _context: IRenderContext): void {
+    header.textContent = this.getDisplayName(entity);
+  }
+
+  /**
+   * Helper to render a single entity header.
+   * Can be used by subclasses that override render() but want consistent header creation.
+   */
+  protected createHeader(entity: T, context: IRenderContext): HTMLElement {
+    const header = document.createElement(this.config.elementTag);
+    header.dataset[this.config.idAttribute] = entity.id;
+    this.renderHeader(entity, header, context);
+    return header;
+  }
+}