fix: resolve cascading renders and optimistic UI race conditions in u…

[Niteshagarwal01]

PR: Fix React Anti-Patterns in useLearningProgress

Closes #606

Title

fix: resolve cascading renders and optimistic UI race conditions in useLearningProgress

Description

Issue:

1. Cascading Renders: The hook previously called setCompletedNodes([]) and setLoading(false) synchronously within the useEffect body when an unauthenticated user was detected. This violated React guidelines and caused the react-hooks/set-state-in-effect linter error.
2. Race Conditions: The toggleNode function employed manual local state updates (Optimistic UI) which conflicted with the onSnapshot listener's built-in latency compensation. This caused duplicate state triggers and potential race conditions if a network update failed.

Fix:

• Derived the fallback empty state dynamically using standard JS ternary operators based on the user context variable instead of firing synchronous state mutations inside the useEffect.
• Removed setLoading(true) from the hook's effect body (as loading initializes to true globally, and the cleanup routine or subsequent onSnapshot adequately manages its transitions).
• Stripped the manual optimistic UI updates from toggleNode, completely deferring to Firestore's native onSnapshot latency compensation which safely handles instantaneous local updates out-of-the-box.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (performance improvements)

Testing

• Ran npx eslint src/hooks/useLearningProgress.ts locally and verified that the react-hooks/set-state-in-effect rule is no longer violated.
• TypeScript compilation passes flawlessly.