docs: align API reference with package surface

[rogerchappel]

Summary

• correct event subscription and push-to-talk/wake method examples
• move fixture file I/O imports to the exported fixture-io subpath
• verify every documented named export and core method against a freshly packed install

Commits

• 593affe test: verify documented API symbols
• b69d952 docs: align API reference with package surface

Verification

• npm ci --ignore-scripts --no-audit --no-fund
• npm run release:check (41 tests, typecheck, build, smoke, installed-package documentation/import checks)
• git diff --check origin/main...HEAD

The strengthened package-import check was confirmed to fail against the prior docs on EVENTS.userSpeechStarted before the documentation correction.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Aligns API documentation with the packed package surface and verifies every documented export plus referenced engine methods in a fresh consumer install (2 files, +41/-9).

Checks run: GitHub CI verify completed SUCCESS; worker verification recorded npm ci --ignore-scripts --no-audit --no-fund, npm run release:check (41/41 tests, typecheck, build, smoke, packed-install documentation verification), and git diff --check origin/main...HEAD; final diff, commit identities, mergeability, branch protection, and head SHA reverified.

Rebased/CI-repaired: No.

Verified head SHA: b69d952c7b3d108d3408c3744b007f76e6d6626a.