feat(run): integrate session origins and agent detection into continuation state

- Update continuation-state to use session_origins from boulder state
- Add isTrackedDescendantSession helper for lineage detection
- Integrate getLastAgentFromSession for reliable agent detection
- Update completion tests for new lineage-aware continuation logic
- Add JSON backend tests for continuation state

🤖 Generated with assistance of OhMyOpenCode

src/cli/run/continuation-state.ts

@@ -1,4 +1,5 @@
 import { getPlanProgress, readBoulderState } from "../../features/boulder-state"
+import { getSessionAgent } from "../../features/claude-code-session-state"
 import {
   getActiveContinuationMarkerReason,
   isContinuationMarkerActive,
@@ -65,6 +66,7 @@ async function hasActiveBoulderContinuation(
   }
 
   const sessionAgent = await getLastAgentFromSession(sessionID, client)
+    ?? getSessionAgent(sessionID)
   if (!sessionAgent) {
     return false
   }