fix(ui): gate voice orb on a true ready signal, not start() returning (#38)

[nithiink]

Fixes #38.

Problem

The voice orb's --amp mic-volume animation began scaling from live mic input before the voice connection was actually ready, across all three providers (Gemini, OpenAI, Azure). The orb gate was keyed on connectedRef, which mirrors connected — and connected flips true the instant s.start() resolves. But start() returns before each provider's post-start application handshake completes, while the mic analyser is already attached. So the moment connected flipped, the orb twitched from mic input during the still-in-progress handshake.

• Gemini: start()/openSocket() return before setupComplete arrives.
• OpenAI/Azure: start() resolves right after setRemoteDescription, but the data channel open → configureSession() fires asynchronously after that. The old code also emitted state: "listening" prematurely at the end of start().

Fix

Introduce an explicit ready transport event emitted at each provider's genuine ready point, and gate the orb on it instead of on start() returning.

• lib/voice.ts — add { type: "ready" } to RealtimeEvent.
• lib/gemini.ts — emit ready on setupComplete.
• lib/realtime.ts — emit ready/listening from the data-channel open handler (after configureSession()), and remove the premature signals at the end of start().
• components/VoiceAgent.tsx — gate orbLoop on a readyRef driven by the ready event instead of connectedRef; reset it in connect()/disconnect().

Comment cleanup

Per review, trimmed the inline comments to remove redundancy: the orb-gate rationale now lives once in lib/orb.ts (its home) and on the ready event in voice.ts; the duplicate restatements in orbLoop, onEvent, and the readyRef declaration were removed or shortened to one-liners.

Tests

Extracted the orb gate/amplitude math into pure helpers (lib/orb.ts: rmsAmp, orbTarget, envelopeStep) so the gate timing is unit-testable, and added lib/orb.test.ts. The core case asserts --amp stays 0 while the gate is closed even under loud mic input, plus envelope decay/rise behavior.

Checks run before opening: node --test (12/12 pass) and tsc --noEmit (clean).

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