docs(telemetry): rename node-health found-ratio and stored-bytes panels

node_reads_hit is a found count, not a cache hit. fetchHitCount_ increments
whenever a fetch returned an object, whatever served it, and a node with
online_delete uses DatabaseRotatingImp which has no NodeObject cache at all. The
ratio therefore reads near 100% while every fetch goes to disk, which made the
cold-read failure mode look impossible on the board.

- Phase9_taskList: node_reads_hit is a found count, not cache-served reads.
- node-health: "NodeStore Cache Hit Ratio" -> "NodeStore Read Found Ratio",
  legends "Cache Hit Ratio" -> "Found Ratio" and "Reads Hit (cache)" ->
  "Reads Found"; corrected the ratio panel's axis label, which read
  "Operations / Sec" on a percentunit panel.
- node-health: "NuDB Storage Size" -> "NuDB Stored Bytes". nudb_bytes observes
  getStoreSize(), the accumulator node_written_bytes also reads, so it is
  cumulative object-payload bytes and not a filesystem measurement.
- ledger-data-sync: point the read-latency discriminator at the renamed panel.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

OpenTelemetryPlan/Phase9_taskList.md

@@ -42,7 +42,7 @@ These metrics serve multiple external consumer categories identified during rese
 
 - In `src/libxrpl/nodestore/Database.cpp`, extend existing `beast::insight` registrations to add:
   - Gauge: `node_reads_total` (cumulative read operations)
-  - Gauge: `node_reads_hit` (cache-served reads)
+  - Gauge: `node_reads_hit` (fetches that found an object — not a cache hit; `fetchHitCount_` increments whatever served the fetch)
   - Gauge: `node_writes` (cumulative write operations)
   - Gauge: `node_written_bytes` (cumulative bytes written)
   - Gauge: `node_read_bytes` (cumulative bytes read)