fix(web): restore button cursor: pointer affordance under Tailwind v4

Tailwind v4 dropped the default cursor: pointer on <button>, so most
interactive controls (bulk sidebar, star/color pickers, summary
disclosures) had no hover affordance. Add a global base rule covering
button / [role=button] / summary, plus cursor: not-allowed for disabled
states to mirror the existing opacity-50 styling.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/app.css

@@ -84,4 +84,20 @@
 		background-color: hsl(var(--background));
 		color: hsl(var(--foreground));
 	}
+
+	/*
+	 * Tailwind v4 dropped the built-in `cursor: pointer` on buttons; restore
+	 * it so every <button>, <summary>, and role="button" gets the click
+	 * affordance. Disabled controls get `not-allowed` so the cursor mirrors
+	 * the visual opacity-50 state already on most buttons.
+	 */
+	button:not(:disabled),
+	[role='button']:not([aria-disabled='true']),
+	summary {
+		cursor: pointer;
+	}
+	button:disabled,
+	[role='button'][aria-disabled='true'] {
+		cursor: not-allowed;
+	}
 }