fix(monitoring): reduce llama-server scrape_interval 15s -> 90s to allow GPU P8 idle

Each /metrics?model=<id> request on the llama.cpp router wakes the GPU
sub-server to P2 (~110W). At 15s with two active jobs (llama3 + phi35),
combined scrape frequency (~7-8s effective) keeps the GPU continuously at
P2 despite zero real inference requests.

At 90s: each scrape wakes GPU for ~5-10s then it drops to P8 (~20W) for
~80s. Verified via iptables block test on 2026-08-13 (t_e7d547ea):
  Before block: 110-115W P2 continuously
  After block:  19-21W P8 consistently
  After unblock: returned to 110W P2 within seconds

qwen3 interval also set to 90s (model not loaded so moot, but consistent).

Ref: t_e7d547ea

cluster/applications/monitoring/values.yaml

@@ -238,8 +238,12 @@ prometheus:
       # jobs — one per model registered in the router — are used so each gets
       # its own model label. The static `model` label is set to the canonical
       # llama.cpp model id (the `id` field from /v1/models, not the alias).
+      # scrape_interval: 90s (reduced from 15s) -- each /metrics?model= request
+      # wakes the GPU sub-server to P2 (~110W); at 15s, continuous spikes kept
+      # the GPU drawing ~110W despite zero inference load. At 90s, the GPU gets
+      # ~80s of genuine P8 idle (~20W) between wake-ups. (t_e7d547ea, 2026-08-13)
       - job_name: llama-server-astro-orbiter-qwen3
-        scrape_interval: 15s
+        scrape_interval: 90s
         metrics_path: /metrics
         params:
           model: ["Qwen3.6-35B-A3B-UD-Q4_K_S"]
@@ -252,7 +256,7 @@ prometheus:
               model: Qwen3.6-35B-A3B-UD-Q4_K_S
 
       - job_name: llama-server-astro-orbiter-llama3
-        scrape_interval: 15s
+        scrape_interval: 90s
         metrics_path: /metrics
         params:
           model: ["Meta-Llama-3.1-8B-Instruct-Q4_K_M"]
@@ -265,7 +269,7 @@ prometheus:
               model: Meta-Llama-3.1-8B-Instruct-Q4_K_M
 
       - job_name: llama-server-astro-orbiter-phi35
-        scrape_interval: 15s
+        scrape_interval: 90s
         metrics_path: /metrics
         params:
           model: ["Phi-3.5-mini-instruct-Q8_0"]