Fix SignInForm error handling and remove unused schedules pages

[jfrench9]

Summary

This PR fixes error handling in the SignInForm component, improving how connectivity and authentication errors are surfaced to users. It also removes the unused ledger schedules pages and performs a subtree split of src/lib/core/.

Changes

🐛 Bug Fix: SignInForm Error Handling

• Refactored error handling logic in SignInForm.tsx to properly catch and display connectivity issues (e.g., network failures, server unreachable) alongside standard authentication errors.
• Updated the component to provide clearer, more actionable error messages to users when sign-in fails due to non-auth reasons.
• Expanded test coverage in SignInForm.test.tsx with new test cases specifically targeting connectivity failure scenarios, ensuring error states render correctly and edge cases are handled.

🗑️ Removed Unused Code

• Deleted src/app/(app)/ledger/schedules/content.tsx (595 lines) and its corresponding page.tsx — these ledger schedule pages were unused and removed as part of cleanup.

🔧 Infrastructure

• Updated CLAUDE.md with minor configuration changes.
• Performed a subtree split of src/lib/core/ into a separate commit for repository organization purposes.

Key UI/UX Improvements

• Users now see meaningful error messages when login fails due to network/connectivity problems instead of generic or missing error feedback.
• Improved distinction between "invalid credentials" errors and "unable to reach server" errors, reducing user confusion during sign-in failures.

Breaking Changes

• Ledger Schedules routes removed: The /ledger/schedules route and all associated components have been deleted. If any navigation links or references point to this route, they will result in a 404. Verify no active features depend on these pages.

Testing Notes for Reviewers

• Run the updated test suite: npm test -- SignInForm.test.tsx — verify all new connectivity error test cases pass.
• Manual testing scenarios:
  1. Sign in with valid credentials → should succeed as before.
  2. Sign in with invalid credentials → should show authentication error message.
  3. Simulate network failure (disable network/block API) → should show connectivity-specific error message.
  4. Simulate server error (500 response) → verify appropriate error handling.
• Confirm /ledger/schedules returns a 404 or redirects appropriately.

Browser Compatibility Considerations

• No new browser APIs or CSS features introduced; changes are limited to error handling logic and test code.
• Error message rendering should be verified across major browsers (Chrome, Firefox, Safari, Edge) to ensure consistent display, particularly for any new conditional UI states in the sign-in form.

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🤖 Generated with Claude Code

Branch Info:

• Source: bugfix/login-fix
• Target: main
• Type: bugfix

Co-Authored-By: Claude noreply@anthropic.com