Test afterAll lifecycle and --ci completion

[DmitrySharabin]

Stacks on #170.

Two-layer regression coverage for #168:

• Unit (Runs at every level, bottom-up, before result.finished resolves) — pins the TestResult finish-listener contract. 3-level nested afterAll with mixed sync/async; asserts bottom-up push order.
• E2E (Completes before process.exit in --ci mode (issue #168)) — spawns node bin/htest.js fixture.js --ci in a subprocess; the fixture's async afterAll writes [test] afterAll ran to stderr, captured and asserted on. Catches env-layer regressions the unit test can't.

Verified by reverting each fix in isolation:

• Revert TestResult.js → unit fails (Got ["level1", "root"], expected ["level2", "level1", "root"]).
• Revert env/node.js → e2e fails (Got false, expected true); unit still passes (independent coverage confirmed).

Test plan

• CI passes

[DmitrySharabin]

Folded into #170, which now contains the fix, these tests, and the docs from #172 as a single squashed commit. The reworked fix dispatches finish after afterAll (matching Mocha/Vitest/Jest convention) — the lifecycle tests here still pass against the new approach.

Closing.