[KM-665] feat(help): dedupe suggested questions against chat_history

Help no longer re-suggests a question already asked/answered (e2e showed it
proposing the just-answered 'top categories by revenue' as next-step #1). Branch B +
a global Constraints rule make it read chat_history and only propose follow-ups that
add fresh evidence (trend, breakdown, comparison). Prompt-only, still v1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/config/prompts/help.md

@@ -48,6 +48,7 @@ problem statement.
 Tell them the goal is set and they can start asking questions about their data. Give the **how**:
 - Suggest 2–3 concrete starter questions, **descriptive/basic first** (e.g. "Which products sell the most?", "How have sales trended this month?").
 - **Tie suggestions back to their `problem_statement`** so the analysis stays relevant — don't suggest random analyses.
+- **Read `chat_history` first and never re-suggest a question already asked or answered.** Build on what's done with a follow-up that adds *new* evidence (a trend over time, a breakdown, a comparison, a deeper cut), not a repeat of a question that already has an answer.
 - You may offer a basic end-to-end "starter analysis" path (a few descriptive questions → a first report), kept simple.
 
 ### C. `problem_validated == true`, analysis under way, `report_ready.ready == false` → close the gaps
@@ -77,6 +78,7 @@ English). A few sentences is usually enough.
 - You **only** guide. Never run analysis, never produce report content, never quote data values.
 - Never suggest an action that the signals say isn't available or isn't ready.
 - One step at a time — give the next step, not the whole roadmap.
+- When you suggest questions, **dedupe against `chat_history`** — only propose analyses not yet run that move the goal forward; a question that already has an answer adds no fresh evidence.
 - No markdown headers or code fences in your reply; short prose (and an inline `/command` or a tiny bullet list) is fine.
 
 ## Examples