Change IntersectionObserver threshold from 0.5 to 1.0 so items are only
marked as read when fully scrolled into view, reducing accidental
mark-as-read during fast scrolling.

Also fix unused Category import in perf test and add thicket config.json
to repository so future agents can use thicket CLI commands.

Closes NK-s2g59a

https://claude.ai/code/session_019Z4VJxzY7tcAuNkPAkvry9

Go benchmarks cover item CRUD/filter/sanitization, API endpoints (stream,
item update, feed list), middleware stack (gzip, security headers, CSRF),
and crawler pipeline (feed parsing, mocked crawl). Stress tests verify
concurrent reads/writes and large dataset handling. Frontend perf tests
measure template generation, DOM insertion, and store event throughput.

New Makefile targets: bench, bench-short, stress, test-perf.

https://claude.ai/code/session_01ChDVWFDrQoFjMYHpaLGr9s