README: document the rebalancer-mode and classic-layer-age options

The askrene-migration work adds two dynamic, setconfig-tunable options
that were not yet covered in the README. Document both next to the
existing rebalancing options:

- clboss-rebalance-mode: classic (default) or off; the entry point for
  the rebalancer mode selector.
- clboss-classic-layer-age-secs: expiration age in seconds (default
  21600) for entries in the persistent clboss askrene layer.

README.md

@@ -565,6 +565,40 @@ Limits the fee CLBOSS will pay for a single internal rebalance.
 The value is in parts-per-million (PPM) of the amount being moved.
 The default is `1000` (0.1% of the amount). Both the
 JitRebalancer and EarningsRebalancer honor this limit.
+
+### `--clboss-rebalance-mode=<classic|off>`
+
+Selects how CLBOSS rebalances channel liquidity:
+
+* `classic` (default): the original CLBOSS rebalancer (JitRebalancer plus
+  EarningsRebalancer), now driven through CLN's `askrene` / `getroutes`
+  pathfinder instead of the deprecated `getroute`.
+* `off`: disable autonomous rebalancing entirely.
+
+This is a *dynamic* option: set it in the `lightningd` config for the
+startup default, or change it at runtime without a restart with
+
+    lightning-cli setconfig clboss-rebalance-mode <mode>
+
+The mode selector is the entry point for future rebalancing strategies;
+`classic` and `off` are the values supported today.
+
+### `--clboss-classic-layer-age-secs=<seconds>`
+
+Sets how long entries persist in the CLBOSS `askrene` layer used by the
+classic rebalancer — the failure / transit feedback recorded by
+FundsMover plus ActiveProber's probe results.  Entries older than this
+cutoff are trimmed once per (roughly hourly) aging pass.
+
+The default is `21600` (six hours).  Because the aging pass runs on a fixed
+cadence, this option sets only the *expiration age*, not how often
+trimming happens; values below roughly one hour do not trim any faster.
+
+This is a *dynamic* option: set it in the `lightningd` config for the
+startup default, or at runtime with
+
+    lightning-cli setconfig clboss-classic-layer-age-secs <seconds>
+
 ### `--clboss-min-nodes-to-process=<number>`
 
 Sets the minimum number of nodes that CLBOSS must know about before it