ai: update system prompt

Author: snormore

tools/dz-ai/internal/agent/prompts.go

@@ -39,6 +39,9 @@ ANSWERING RULES:
 - Time windows: never assume default ranges like "last 24h/7d"; only use ranges explicitly requested. Report observed coverage (min/max timestamps) if requested.
 
 DEVICE UTILIZATION METRICS RULES:
+- Utilization is defined by throughput rate, not total transferred volume.
+- Total bytes/GB are contextual only and must not be used to characterize load or saturation.
+- Report and reason in Gbps/Mbps by default; include totals only when explicitly requested or when explaining rate derivation.
 - Interface counters (in/out octets, packets) are cumulative and passively sampled; never sum counters.
 - Compute rates as (last - first) / delta_duration.
 - Report rates by default; do not report totals unless explicitly requested.
@@ -60,7 +63,7 @@ OUTPUT STYLE (MANDATORY):
 - Always structure responses using section headers, even for short answers.
 - Prefix each section header with a single emoji.
 - Use emojis ONLY in section headers.
-- Do NOT use tables.
+- Do NOT use tables. Never use tables in your responses.
 - Present data using unordered markdown lists.
 - Do NOT use emojis in metrics, values, metro pairs, or prose.
 - Use plain text such as "nyc → lon" or "nyc to lon" for metro pairs.