Adds header drawer and event drag interactions

Introduces HeaderDrawerRenderer and HeaderDrawerLayoutEngine to support dragging events into an all-day header drawer

Enables dynamic event placement and conversion between timed and all-day events through new drag interactions
Implements flexible layout calculation for header items with column and row management

Extends DragDropManager to handle header zone interactions
Adds new event types for header drag events

src/v2/features/headerdrawer/HeaderDrawerLayoutEngine.ts

@@ -0,0 +1,135 @@
+/**
+ * HeaderDrawerLayoutEngine - Calculates row placement for header items
+ *
+ * Prevents visual overlap by assigning items to different rows when
+ * they occupy the same columns. Uses a track-based algorithm similar
+ * to V1's AllDayLayoutEngine.
+ *
+ * Each row can hold multiple items as long as they don't overlap in columns.
+ * When an item spans columns that are already occupied, it's placed in the
+ * next available row.
+ */
+
+export interface IHeaderItemLayout {
+  itemId: string;
+  gridArea: string;        // "row / col-start / row+1 / col-end"
+  startColumn: number;
+  endColumn: number;
+  row: number;
+}
+
+export interface IHeaderItemInput {
+  id: string;
+  columnStart: number;     // 0-based column index
+  columnEnd: number;       // 0-based end column (inclusive)
+}
+
+export class HeaderDrawerLayoutEngine {
+  private tracks: boolean[][] = [];
+  private columnCount: number;
+
+  constructor(columnCount: number) {
+    this.columnCount = columnCount;
+    this.reset();
+  }
+
+  /**
+   * Reset tracks for new layout calculation
+   */
+  reset(): void {
+    this.tracks = [new Array(this.columnCount).fill(false)];
+  }
+
+  /**
+   * Calculate layout for all items
+   * Items should be sorted by start column for optimal packing
+   */
+  calculateLayout(items: IHeaderItemInput[]): IHeaderItemLayout[] {
+    this.reset();
+    const layouts: IHeaderItemLayout[] = [];
+
+    for (const item of items) {
+      const row = this.findAvailableRow(item.columnStart, item.columnEnd);
+
+      // Mark columns as occupied in this row
+      for (let col = item.columnStart; col <= item.columnEnd; col++) {
+        this.tracks[row][col] = true;
+      }
+
+      // gridArea format: "row / col-start / row+1 / col-end"
+      // CSS grid uses 1-based indices
+      layouts.push({
+        itemId: item.id,
+        gridArea: `${row + 1} / ${item.columnStart + 1} / ${row + 2} / ${item.columnEnd + 2}`,
+        startColumn: item.columnStart,
+        endColumn: item.columnEnd,
+        row: row + 1  // 1-based for CSS
+      });
+    }
+
+    return layouts;
+  }
+
+  /**
+   * Calculate layout for a single new item
+   * Useful for real-time drag operations
+   */
+  calculateSingleLayout(item: IHeaderItemInput): IHeaderItemLayout {
+    const row = this.findAvailableRow(item.columnStart, item.columnEnd);
+
+    // Mark columns as occupied
+    for (let col = item.columnStart; col <= item.columnEnd; col++) {
+      this.tracks[row][col] = true;
+    }
+
+    return {
+      itemId: item.id,
+      gridArea: `${row + 1} / ${item.columnStart + 1} / ${row + 2} / ${item.columnEnd + 2}`,
+      startColumn: item.columnStart,
+      endColumn: item.columnEnd,
+      row: row + 1
+    };
+  }
+
+  /**
+   * Find the first row where all columns in range are available
+   */
+  private findAvailableRow(startCol: number, endCol: number): number {
+    for (let row = 0; row < this.tracks.length; row++) {
+      if (this.isRowAvailable(row, startCol, endCol)) {
+        return row;
+      }
+    }
+
+    // Add new row if all existing rows are occupied
+    this.tracks.push(new Array(this.columnCount).fill(false));
+    return this.tracks.length - 1;
+  }
+
+  /**
+   * Check if columns in range are all available in given row
+   */
+  private isRowAvailable(row: number, startCol: number, endCol: number): boolean {
+    for (let col = startCol; col <= endCol; col++) {
+      if (this.tracks[row][col]) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Get the number of rows currently in use
+   */
+  getRowCount(): number {
+    return this.tracks.length;
+  }
+
+  /**
+   * Update column count (e.g., when view changes)
+   */
+  setColumnCount(count: number): void {
+    this.columnCount = count;
+    this.reset();
+  }
+}