fix: nlpStartOf() sets time to 00:00 instead of 23:59

[vipul674]

Summary

• Fixed nlpStartOf() in server.js to set time to 00:00:00 instead of 23:59:00
• All NLP-extracted task due dates now correctly use start-of-day timestamps

Problem

The nlpStartOf() helper was setting d.setHours(23, 59, 0, 0) — the end of the day — despite its name implying start-of-day. This caused every task extracted via the NLP fallback parser to have due_at at 23:59 instead of 00:00.

Fix

// Before
d.setHours(23, 59, 0, 0);

// After
d.setHours(0, 0, 0, 0);

Impact

• Task sorting and calendar display now use correct start-of-day semantics
• Deadline comparisons work as expected for NLP-extracted tasks
• Affects the NLP fallback path (when Gemini API is unavailable or fails)

Fixes #923

[vipul674]

@Charushi06 please review the pr

[vipul674]

@Charushi06 review reminder