refactor(webstreams): fix layer boundaries and extract EncryptTransform

[imaTik0]

Move service/ types into their owning layer:

• src/service/EventDispatcher.ts → src/webStreams/EventDispatcher.ts (fix removeOnStateChangeListener filter, add JSDoc, wrap emit in try/catch)
• src/service/WebRtcInterface.ts → src/webStreams/WebRtcInterface.ts (remove server event types that belong in native layer; add WebRtcMethodCall discriminated union; import Jsep from ApiTypes)

ApiTypes.ts:

• Add Jsep interface (sdp + RTCSdpType) replacing the loose string in WebRtcInterface
• Add StreamTrack interface (replaces StreamApi-local definition)
• Remove dead types: StreamRemoteInfo, StreamList, StreamTrackList, PublishMeta, TrackInfo, StreamRoomInfo, StreamRoomList, TrackType

WebRtcInterfaceImpl.ts:

• Update import paths to new locations
• Replace { [K: string]: Function } methodsMap with typed MethodMap
• Fix method bindings with .bind(this) and typed lambda for updateSessionId
• methodCall now uses WebRtcMethodCall["name"] as key type

EncryptTransform.ts (new src/webStreams/worker/):

• Extract per-frame AES-256-GCM logic out of the monolithic worker.ts
• Pure class: no worker globals, no postMessage, no module state
• encryptFrame takes lastRms as a parameter; decryptFrame returns rms | null

worker.ts:

• Use EncryptTransform and new WorkerEvents discriminated unions
• Add RTCRtpScriptTransform entry point (modern browsers) alongside postMessage
• Add stop operation with AbortController-based pipeline cancellation
• logPipelineError ignores AbortError in addition to "Destination stream closed"

KeyStore.ts:

• Make setKeys async (was fire-and-forget; importKeyAndWipeMaterial is async)
• Add getEncryptionExternalKeyId() and resolveKeyId() stubs (same value as getEncryptionKeyId for now; session-prefix refactor comes later)

Add EncryptTransform.test.ts covering audio/video encrypt+decrypt round-trips, header preservation, tamper detection, and short-frame passthrough.