feat(rpc): add GetMoleculeProgress endpoint (bd-0oqz)

New RPC endpoint to get detailed progress for a molecule (parent issue
with child steps). Returns moleculeID, title, assignee, and list of
steps with their status (done/current/ready/blocked) and timestamps.

Used when user expands a worker in the activity feed TUI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/rpc/server_routing_validation_diagnostics.go

@@ -219,6 +219,8 @@ func (s *Server) handleRequest(req *Request) Response {
 		resp = s.handleEpicStatus(req)
 	case OpGetMutations:
 		resp = s.handleGetMutations(req)
+	case OpGetMoleculeProgress:
+		resp = s.handleGetMoleculeProgress(req)
 	case OpGetWorkerStatus:
 		resp = s.handleGetWorkerStatus(req)
 	case OpShutdown: