fix(nlp): add support for "end of year" date parsing in fallback extractor

[shivambind269-ai]

Related Issue

Closes #675

Summary

Adds support for parsing the phrase "end of year" in the server-side NLP fallback extractor when the Gemini API is unavailable.

Changes Made

• Added regex handling for "end of year" and "end of the year" inside nlpExtractDate()
• Aligned backend fallback behavior with frontend NLP parsing logic
• Ensured deadlines correctly resolve to December 31 of the current year

Testing

• Tested locally by disabling GEMINI_API_KEY
• Verified that phrases like "Submit report by end of year" now resolve correctly
• Confirmed existing date parsing behavior remains unchanged

Screenshots

No UI changes.

Checklist

• Code follows project style
• Tested locally
• No unrelated changes included
• Documentation updated (if applicable)