fix(web): make microphone startup failure-atomic

[rogerchappel]

Summary

• release microphone tracks and all partially initialized Web Audio resources when start() fails
• keep cleanup best-effort so the original classified microphone error and cause remain observable
• cover AudioContext construction and later analyser setup failures, including zero retained timers/resources
• document the failed-start lifecycle guarantee

Commits

• 0670441 fix(web): make microphone start failure-atomic
• ca8e93b docs(web): document failed-start cleanup guarantee

Verification

• npm ci
• npm test (37 passed)
• npm run lint --if-present
• npm run build --if-present
• git diff --check origin/main..HEAD
• verified every proposed commit author and committer is Roger Chappel <miscanalysis@gmail.com>