Fix exported subtitle word sync

[nickbeau]

Summary

• Shift exported subtitle word highlighting 500 ms later so it matches the speaker.
• Calibrate the streaming recognizer delay to one second.
• Update the focused regression test for the corrected timestamps.

Validation

• npm audit --audit-level=high: passed; 0 vulnerabilities
• npm test: passed; 57 tests
• npm run typecheck: passed
• npm run speech:smoke: passed under a compatible x64 Node runtime
• npm run build:desktop: passed

Notes

• The active shell uses ARM64 Node 26, while the installed Sherpa native package is x64. The speech smoke test was therefore rerun successfully with the bundled x64 Node runtime; GitHub CI uses supported Windows x64 Node 22.12.
• No migration or rollout steps are required.