HTTP plans list: unbounded `ListGoals` then slice; `GetPlan` errors silently dropped

[mrchatam]

• Label: bug
• Severity: degrades quality
• Location: internal/httpapi/handlers_p1.go (~defaultPlanListGoalLimit, plan list handler):

  goals, err := st.ListGoals()   // unbounded — store.ListGoals → ListGoalsLimited(-1)
  ...
  if len(goals) > limit {
      truncated = true
      goals = goals[:limit]
  }
  for _, g := range goals {
      view, err := ps.GetPlan(r.Context(), g.ID)
      if err != nil {
          continue   // swallow
      }
      items = append(items, view)
  }
  writeJSON(..., {"items": items, "count": len(items), "truncated": truncated})

• Expected: SQL/keyset-limited goal page; plan load failures surface as errors (or explicit skipped[]), and count/truncated reflect honesty.
• Actual: Residual load-all-then-slice. Any GetPlan failure omits that goal with no error, so clients can see count < requested slice with truncated: false and believe the graph is complete. Prior QA residual confirmed still present on this tip.

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Audited tip: 6afe0fd (main). Filed from independent Phase 1 code audit 2026-09-19.