clboss-xrebalance-view: add an On column showing peer online/offline

Adds an "On" column immediately after the opener "O" column: "." when the
peer is connected, "X" when it is offline. Sourced from listpeerchannels'
peer_connected field. Offline peers cannot be rebalanced through, so flagging
them makes it obvious why a suggested source/dest endpoint is unreachable.

The TOTALS rows and CSV output are updated to keep column alignment.

contrib/clboss-xrebalance-view

@@ -224,6 +224,8 @@ def compute_row(channel, peer, window_days):
         "alias": peer.get("alias") or "",
         "scid": channel.get("scid"),
         "opener": "L" if channel.get("opener") == "local" else "R",
+        # '.' connected, 'X' offline -- offline peers can't be rebalanced through
+        "online": "." if channel.get("peer_connected") else "X",
         "cap_sat": cap_sat,
         "pct_local": pct_local,
         "local_sat": local_sat,
@@ -380,6 +382,7 @@ def main():
             "scid": scid,
             "peer_id": peer_id,
             "opener": ch.get("opener"),
+            "peer_connected": ch.get("peer_connected", False),
             "to_us_msat": ch.get("to_us_msat", 0),
             "total_msat": ch.get("total_msat", 0),
         }
@@ -473,7 +476,7 @@ def main():
     rows.sort(key=sort_keys[args.sort])
 
     headers = [
-        "Alias", "SCID", "O",
+        "Alias", "SCID", "O", "On",
         "Cap sat", "Loc %", "LocalBal", "RemoteBal", "TgtFill", "TgtDrain",
         "Age d", "Ops d",
         "InFwd sat", "InEarn", "InExp", "InNet", "InPpm", "InNetPpm",
@@ -485,6 +488,7 @@ def main():
             r["alias"],
             r["scid"],
             r["opener"],
+            r["online"],
             fmt_int(r["cap_sat"]),
             fmt_pct(r["pct_local"]),
             fmt_int(r["local_sat"]),
@@ -539,6 +543,7 @@ def main():
             pad_string(label, max_alias),    # Alias
             f"n={len(subset)}",              # SCID (reused for count)
             "",                              # O
+            "",                              # On
             fmt_int(total_cap),              # Cap sat
             "",                              # Loc %
             fmt_int(total_local),            # LocalBal