Update AGENTS.md + bootstrap with diagnostic-first rule on data/chart bugs (Richie redirected twice in 2wks)

Update AGENTS.md + bootstrap with diagnostic-first rule on data/chart/production bugs. CARRY-FORWARD from 2026-06-16 reflection (memory/2026-06-16.md, priority 1). Richie redirected me on this pattern TWICE in two weeks: - ~2 weeks back: Smartcar rate-limit hypothesis from code structure - 2026-06-15 22:00 UTC: V-notch root-cause hypothesis from code structure Both times Richie asked: "Can't you locally do the debug/diagnostic yourself?" In both cases the hypothesis was wrong and a 5-min readonlyPrisma query against source-of-truth data resolved it correctly. Pattern is now owed a STRUCTURAL fix, not "I'll remember." Implementation: 1. Add section to AGENTS.md under "Investigations / Data bugs": - Rule: For any chart/data/production-behavior question, the FIRST action is a diagnostic query against source-of-truth data (readonlyPrisma, Datadog, S3, etc.), NOT a hypothesis paragraph from code structure. - Violations: shipping a hypothesis BEFORE a diagnostic query. - Counter-example: V-notch 2026-06-15 (correct: pull 24h CAGG state, confirm timestamps align, identify per-band zero-crossings) 2. Update bootstrap checklist to include "diagnostic-query-first on data bugs" as an enumerated pre-flight category. 3. Add to LEARNINGS.md as a structural rule born 2026-06-16. Acceptance: AGENTS.md has the rule, bootstrap surfaces it, next data/chart investigation lead with a query not a hypothesis. Priority 1.