fix: Add missing setTooltip mock to fix failing tests

Add setTooltip function mock to the Obsidian API test mock to match
the native tooltip functionality recently introduced in the codebase.
This resolves all TaskCard test failures caused by missing mock implementation.

- Adds setTooltip mock with same signature as Obsidian's native function
- Includes proper tooltip attribute setting for test verification
- Exports setTooltip in both named and default exports for compatibility

Fixes 39 failing TaskCard tests.

tests/__mocks__/obsidian.ts

@@ -857,6 +857,16 @@ export function setIcon(element: HTMLElement, iconName: string): void {
   element.classList.add('has-icon');
 }
 
+// Tooltip utilities
+export function setTooltip(element: HTMLElement, tooltip: string, options?: { placement?: string }): void {
+  // Mock implementation - just add tooltip attributes
+  element.setAttribute('data-tooltip', tooltip);
+  if (options?.placement) {
+    element.setAttribute('data-tooltip-placement', options.placement);
+  }
+  element.classList.add('has-tooltip');
+}
+
 // Keymap mock class
 export class Keymap {
   pushScope = jest.fn();
@@ -924,6 +934,7 @@ export const MockObsidian = {
   Menu,
   Notice,
   setIcon,
+  setTooltip,
 };
 
 // Default export for compatibility
@@ -953,6 +964,7 @@ export default {
   Notice,
   Events,
   setIcon,
+  setTooltip,
   parseLinktext,
   MockObsidian,
 };