feat: add context compaction to automatically summarize old messages (#compaction) (#276)

When input tokens exceed a configurable threshold after a conversation round,
the system asynchronously compacts older messages into a summary. Cascading
compactions reference prior summaries via <prior_context> tags to maintain
conversational continuity without duplicating content.

- Add bot_history_message_compacts table and compact_id on messages
- Add compaction_enabled, compaction_threshold, compaction_model_id to bots
- Implement compaction service (internal/compaction) with LLM summarization
- Integrate into conversation flow: replace compacted messages with summaries
  wrapped in <summary> tags during context loading
- Add REST API endpoints (GET/DELETE /bots/:bot_id/compaction/logs)
- Add frontend Compaction tab with settings and log viewer
- Wire compaction service into both dev (cmd/agent) and prod (cmd/memoh) entry points
- Update test mocks to include new GetBotByID columns

internal/message/service.go

@@ -482,7 +482,7 @@ func toMessageFromSinceBySessionRow(row sqlc.ListMessagesSinceBySessionRow) Mess
 }
 
 func toMessageFromActiveSinceRow(row sqlc.ListActiveMessagesSinceRow) Message {
-	return toMessageFields(
+	m := toMessageFields(
 		row.ID,
 		row.BotID,
 		row.SessionID,
@@ -499,10 +499,14 @@ func toMessageFromActiveSinceRow(row sqlc.ListActiveMessagesSinceRow) Message {
 		row.Usage,
 		row.CreatedAt,
 	)
+	if row.CompactID.Valid {
+		m.CompactID = row.CompactID.String()
+	}
+	return m
 }
 
 func toMessageFromActiveSinceBySessionRow(row sqlc.ListActiveMessagesSinceBySessionRow) Message {
-	return toMessageFields(
+	m := toMessageFields(
 		row.ID,
 		row.BotID,
 		row.SessionID,
@@ -519,6 +523,10 @@ func toMessageFromActiveSinceBySessionRow(row sqlc.ListActiveMessagesSinceBySess
 		row.Usage,
 		row.CreatedAt,
 	)
+	if row.CompactID.Valid {
+		m.CompactID = row.CompactID.String()
+	}
+	return m
 }
 
 func toMessageFromLatestRow(row sqlc.ListMessagesLatestRow) Message {

internal/message/types.go

@@ -36,6 +36,7 @@ type Message struct {
 	Metadata                map[string]any  `json:"metadata,omitempty"`
 	Usage                   json.RawMessage `json:"usage,omitempty"`
 	Assets                  []MessageAsset  `json:"assets,omitempty"`
+	CompactID               string          `json:"compact_id,omitempty"`
 	CreatedAt               time.Time       `json:"created_at"`
 }