Fix cross-network block detection and remove false orphan artifacts

- Change OrphanedAt from time.Time to *time.Time so JSON omitempty
  correctly omits zero values (Go serializes zero time.Time as
  "0001-01-01T00:00:00Z" which JS treats as truthy)
- Rewrite reconcileOnce with 4-pass architecture: enrichment, reorg
  detection via GetBlock verification, false-positive un-orphaning,
  and legacy block stamping
- Use inferOtherChain() to stamp cross-network blocks with the correct
  chain identifier (testnet4 reports as "testnet4", not "test")
- Move tailer startup after aggregator's first refresh so blocks are
  always stamped with the current chain
- Add StampChain store method, debug-blocks admin endpoint, and
  comprehensive reconcile tests for cross-network scenarios

api/internal/httpapi/server.go

@@ -37,6 +37,7 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /api/blocks", s.blocks)
 	mux.HandleFunc("GET /api/snapshot", s.snapshot)
 	mux.HandleFunc("GET /api/ws", s.handleWS)
+	mux.HandleFunc("GET /api/admin/debug-blocks", s.debugBlocks)
 	mux.Handle("/", spaHandler(webui.FS()))
 	return mux
 }
@@ -159,3 +160,51 @@ func (s *Server) clients(w http.ResponseWriter, r *http.Request) {
 func (s *Server) blocks(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, s.Agg.Blocks())
 }
+
+// debugBlocks exposes raw block state from both the in-memory snapshot
+// (what the UI sees) and the DB (ground truth) for troubleshooting.
+func (s *Server) debugBlocks(w http.ResponseWriter, r *http.Request) {
+	type row struct {
+		Height     int64   `json:"height"`
+		Hash       string  `json:"hash"`
+		Chain      string  `json:"chain"`
+		OrphanedAt string  `json:"orphaned_at"`
+		FoundAt    string  `json:"found_at"`
+		RewardBTC  float64 `json:"reward_btc"`
+		Source     string  `json:"source"`
+	}
+	fmtBlock := func(b state.BlockRecord) row {
+		orphaned := ""
+		if b.OrphanedAt != nil {
+			orphaned = b.OrphanedAt.Format("2006-01-02T15:04:05Z")
+		}
+		return row{
+			Height:     b.Height,
+			Hash:       b.Hash,
+			Chain:      b.Chain,
+			OrphanedAt: orphaned,
+			FoundAt:    b.FoundAt.Format("2006-01-02T15:04:05Z"),
+			RewardBTC:  b.RewardBT,
+			Source:     b.Source,
+		}
+	}
+
+	// In-memory blocks (what /api/blocks and /api/snapshot serve)
+	memBlocks := s.Agg.Blocks()
+	mem := make([]row, 0, len(memBlocks))
+	for _, b := range memBlocks {
+		mem = append(mem, fmtBlock(b))
+	}
+
+	// DB blocks (ground truth)
+	dbBlocks := s.Agg.BlocksFromStore()
+	db := make([]row, 0, len(dbBlocks))
+	for _, b := range dbBlocks {
+		db = append(db, fmtBlock(b))
+	}
+
+	writeJSON(w, http.StatusOK, map[string]any{
+		"memory": mem,
+		"db":     db,
+	})
+}