feat(tools): add get_current_time tool

[Antiarin]

Description

Add get_current_time MCP tool so agents can fetch accurate current time, especially useful in long-running sessions where system prompt time goes stale.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

Fixes #3292

Changes Made

• Add time_tool/ with get_current_time tool
• Supports any IANA timezone (UTC, America/New_York, Asia/Kolkata, etc.)
• Returns: datetime, date, time, timezone, day_of_week, unix_timestamp
• Error handling for invalid timezones
• Comprehensive test suite (14 tests)

Testing

• Unit tests pass (PYTHONPATH=core:tools/src pytest tools/tests/tools/test_time_tool.py -v)
• Lint passes (make check)
• Manual testing performed

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Antiarin]

@RichardTang-Aden @TimothyZhang7 @bryanadenhq ->ready for review when you get a chance!