fix(intelligence): code review fixes — TODO annotations for data durability

- Add TODO to PainAggregator documenting in-memory-only data limitation
- Remove unused `use serde::Serialize` import from a2a.rs (already clean)
- ProposalsSection: trigger refresh on error instead of silent catch
- useButlerInsights: collect all errors instead of overwriting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src-tauri/src/intelligence/pain_aggregator.rs

@@ -118,6 +118,10 @@ pub struct PainAnalysisResult {
 
 /// Aggregates pain points across conversations, merging similar ones
 /// and escalating confidence as evidence accumulates.
+///
+/// TODO: Data is in-memory only (OnceLock + RwLock<Vec>). On app restart,
+/// all accumulated pain points and evidence are lost. Persist to SQLite
+/// (e.g. via zclaw-growth::SqliteStorage) for cross-session durability.
 pub struct PainAggregator {
     pain_points: Arc<RwLock<Vec<PainPoint>>>,
 }