Introduce `_seed_gist_with_comments`, `_seed_news_with_comments`, and `_seed_project_with_comments` helper functions that create a user, a parent entity, and four comments (excluded, flat, parent, reply) with a shared marker prefix and timestamps, enabling consistent comment tree seeding across test modules.
Split the monolithic test directory into three tiers (unit, api, e2e) with a path-mirroring directory structure. Added corresponding Makefile targets (test-unit, test-api, test-e2e) and updated all documentation references (CLAUDE.md, README.md, testing-cicd.html, testing-framework.html, testing-make.html) to reflect the new layout and naming conventions.
