Fix command history pagination resets - #53

Summary

Stabilize pagination on the workspace command activity/history page.

Root cause

Changing page changes the React Query key. While the new page is loading, commandQuery.data was temporarily undefined, so the page derived totalPages = 1. The clamp effect then immediately reset any requested page > 1 back to page 1 before the fetch completed.

Fix

• keep previous command-history data while a pagination query is loading
• skip page clamping while React Query is serving placeholder data
• preserve the existing clamp once a real response confirms that the current page no longer exists
• add regression tests for placeholder-data navigation and real-page clamping

Validation

• targeted Vitest: 8/8 passed
• tsc --noEmit --project tsconfig.json passed
• git diff --check passed

Closes #52