feat(server+tui): event bridge — live streaming and historical replay

- SessionEventBridge: replaySnapshot() sends all historical events on connect;
  streamLive(sessionId) subscribes to live event flow per session
- DomainEventMapper: maps 14 domain event types to ServerMessage; reads
  InferenceCompleted response text from ArtifactStore with empty-string fallback
- GlobalStreamHandler: wires bridge on connect for replay, launches per-session
  live-stream job on StartSession, cancels all jobs on disconnect; removes
  ProtocolError("ping") heartbeat hack
- SessionStreamHandler: fixes replay to use DomainEventMapper instead of
  emitting SessionStarted for every event; injects real artifactStore;
  removes ProtocolError("ping") heartbeat; adds structured logging throughout
- Main: startup log block showing port, model config, sandbox, stores, tools,
  providers
- SessionsReducer: StageCompleted/StageFailed now clears currentStage; adds
  5 missing tests (InferenceCompleted, StageStarted, ToolCompleted, SessionPaused)
- RouterPanel: new TUI widget rendering active session's lastResponseText
- TuiWsClient: remove println that was polluting the TUI on WS connect failure

apps/server/build.gradle

@@ -43,6 +43,8 @@ dependencies {
     implementation "io.ktor:ktor-server-status-pages:$ktor_version"
     implementation "io.ktor:ktor-server-call-logging:$ktor_version"
 
+    testImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:$kotlinx_coroutines_version"
+
     implementation "org.apache.logging.log4j:log4j-core:2.24.1"
     implementation "org.apache.logging.log4j:log4j-slf4j2-impl:2.24.1"
     implementation "org.slf4j:slf4j-api:2.0.16"