docs: Deduplicate validate-check helper

Keep a single Makefile validate-check target that prints the full
/metrics dump, highlights hit/miss fields, and curls /lancache-heartbeat.
Drop the duplicate README troubleshooting item and align the validation
chapter plus validate-config.yaml comments with that behavior.

Link: #29

README.md

@@ -59,11 +59,12 @@ After steamcache2 is running (default `listen_address: :80`) and has seen a litt
 
 ```bash
 make validate-check
-# or:
+# or, manually:
 curl -s http://localhost/metrics
+curl -s -i http://localhost/lancache-heartbeat
 ```
 
-Read these fields:
+`make validate-check` prints the full `/metrics` dump, highlights hit/miss fields, and curls `/lancache-heartbeat`. Read these fields:
 
 | Field | Meaning |
 | --- | --- |
@@ -128,12 +129,13 @@ When the server is running, point your external SteamPrefill (or other load gene
 ./SteamPrefill benchmark run ...
 ```
 
-When finished, you can get a quick metrics summary with:
+When finished, you can get a quick metrics + heartbeat report with:
 
 ```bash
 make validate-check
-# or:
+# or, manually:
 curl -s http://localhost/metrics
+curl -s -i http://localhost/lancache-heartbeat
 ```
 
 See [Quick check: is it caching?](#quick-check-is-it-caching) for which fields to read. This is the recommended simple workflow. No automatic downloading or running of external tools.
@@ -144,16 +146,17 @@ After a benchmark run you can ask for a quick report:
 
 ```bash
 make validate-check
-# or manually:
+# or, manually:
 curl -s http://localhost/metrics
+curl -s -i http://localhost/lancache-heartbeat
 ```
 
-Look for:
+`make validate-check` prints the full `/metrics` dump, highlights hit/miss fields, and curls `/lancache-heartbeat`. Look for:
 - High cache hit rate after the warmup pass (`cache_hits`, `hit_rate`, plus `memory_cache_hits` / `disk_cache_hits`)
 - Non-zero `coalesced` and `disk` activity
 - Zero unexpected `errors`
 
-Heartbeat is the same as the operator check: `curl -s -i http://localhost/lancache-heartbeat` (HTTP 204, `X-LanCache-Processed-By: SteamCache2`).
+Heartbeat should be HTTP 204 with `X-LanCache-Processed-By: SteamCache2`. Use GET (`curl -i`), not HEAD (`curl -I`).
 
 #### The Validation Config
 
@@ -409,12 +412,7 @@ make
    - Adjust the disk cache size to match available storage
 
 6. **Not sure if it is caching**
-   - Do not start with the full SteamPrefill chapter. Use [Quick check: is it caching?](#quick-check-is-it-caching): `make validate-check` or `curl -s http://localhost/metrics`
-   - `cache_misses` on the first request is expected; a repeat of the same object should increment `cache_hits`
-   - `curl -si http://localhost/lancache-heartbeat` should return 204 and `X-LanCache-Processed-By: SteamCache2`
-
-6. **Not sure if it is caching**
-   - See [Quick check: is it caching?](#quick-check-is-it-caching): `make validate-check` or `curl -s http://localhost/metrics`
+   - Do not start with the full SteamPrefill chapter. Use [Quick check: is it caching?](#quick-check-is-it-caching): `make validate-check` (full `/metrics`, hit/miss fields, and `/lancache-heartbeat`)
    - A first pass is mostly `cache_misses`; repeating the same content should raise `cache_hits` / `hit_rate`
    - Confirm the process is up with `curl -s -i http://localhost/lancache-heartbeat` (GET, not HEAD)