feat: noise suppression, 88 tests, real-time translation, improved account UX #4769 — ccantynz/voxlen

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/32

Summary

Audio noise suppression — high-pass biquad filter (80 Hz) + noise gate (-40 dBFS) applied in the capture pipeline. Removes desk vibration, HVAC hum, and background noise before audio reaches Deepgram. Input gain setting now actually applied.
88 tests passing — Vitest setup, tests for clients store, flywheel store, context formatters, smart format, voice commands, export utils. First test coverage in the project.
Real-time translation — translate transcribed text to any target language after grammar correction (from parallel agent, pending merge into this branch).
Account tab UX overhaul — clean sign-in/sign-out card instead of raw API key input. Shows "Get your API key at voxlen.ai" CTA when not connected, green connected state when linked.
Per-client matter tracking — clients store with billable time auto-recorded per dictation session (landed in #31, tests added here).

Start dictation in a noisy environment — background hum should be reduced vs previous version
Open Settings → Account — should show sign-in card with purple CTA button
Enter a Voxlen API key → should show green "Connected" state
Run npm test — all 88 tests should pass
cargo check — no Rust errors

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