test: add coverage for _cut lookup text trimming

[CaptainLevi25]

What & why

Summary

Resolves #73

Add focused tests for _cut in taskuary/lookups.py.

What changed

• Added a new CutTests test class in tests/test_lookups.py.
• Covered whitespace and newline collapsing below the 600-character threshold.
• Covered preservation of existing lines at and above 600.
• Covered the exact-length boundary where text should not be cut.
• Covered truncation with the […] suffix.
• Covered None returning an empty string.

Screenshot for tests/test_lookups.py

Test Cases increased from 15 -> 21 and all passes

😔 Expectation not met

please note while running all the test using python -m pytest -q.
I faced error in 3 test suites out of all which had module import error since it required a module from tests/test_funnel itself

Checklist

• python -m pytest -q passes (offline, no credentials)
• New behavior has a test (Timeline/Board/Review chips: a named picture from taskuary.testing)
• UI touched → taskuary/web/ rebuilt & committed, render_check.mjs clean, screenshot below
• README updated if users can see the change