fix: audit round 3 — IDOR report-scoping, auth rate-limit, briefing chat scoping, DailyVolumes dedup, N+1 list routines, FE export/ask error handling

- IDOR: interrogate without report_id now scoped to user_key (LatestReportForUser); regression test TestInterrogateIDORScoped
- auth: signup/login per-IP rate limit 10/60s (new internal/api/ratelimit.go) + test
- chat unscoped grounding: build caller's own briefing instead of global LatestBriefing
- DailyVolumes: dedupe by bar date (snapshot rows hold 30-day windows) — fixes volume-anomaly skew
- GetDestination: direct (id,user_key) query instead of listing all
- ListRoutines: single LastRunsByRoutine query instead of N+1 RunHistory
- FE: exportMd/ask/HTML/PDF export now surface errors; alerts create clears channels

backend/internal/api/routines.go

@@ -28,11 +28,16 @@ func (s *Server) ListRoutines(w http.ResponseWriter, r *http.Request) {
 		LastRun any `json:"last_run"`
 	}
 	out := make([]rowOut, 0, len(rows))
+	lastByRoutine, lerr := s.DB.LastRunsByRoutine(s.userKey(r))
+	if lerr != nil {
+		lastByRoutine = nil
+	}
 	for _, row := range rows {
-		hist, _ := s.DB.RunHistory(row.ID, 1)
 		var last any
-		if len(hist) > 0 {
-			last = hist[0]
+		if lastByRoutine != nil {
+			if v, ok := lastByRoutine[row.ID]; ok {
+				last = v
+			}
 		}
 		out = append(out, rowOut{row, last})
 	}