feat: comprehensive INFO/WARN/ERROR logging across all controller modules

Add structured operational logging at INFO, WARN, and ERROR levels to
every controller module. Standardize custom prefixes ([GEO], [SCHED],
[SYNC]) to use [INFO/WARN/ERROR] [module] format. Fix misleveled logs
(WARN->ERROR for data loss scenarios, WARN->INFO for routine operations).

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

controller/internal/backup/backup.go

@@ -856,6 +856,7 @@ func (m *Manager) perDriveRepoStats() []DriveRepoInfo {
 		}
 		stats, err := m.restic.Stats(repoPath)
 		if err != nil {
+			m.logger.Printf("[WARN] [backup] perDriveRepoStats: failed to get stats for %s: %v", drive, err)
 			continue
 		}
 		infos = append(infos, DriveRepoInfo{
@@ -866,6 +867,7 @@ func (m *Manager) perDriveRepoStats() []DriveRepoInfo {
 			LatestSnapshot: stats.LatestSnapshot,
 		})
 	}
+	m.logger.Printf("[INFO] [backup] perDriveRepoStats: collected stats for %d drives", len(infos))
 	return infos
 }
 
@@ -918,6 +920,7 @@ func (m *Manager) aggregateRepoStats() *RepoStats {
 	if totalBytes > 0 {
 		agg.TotalSize = humanizeBytes(totalBytes)
 	}
+	m.logger.Printf("[INFO] [backup] Aggregated repo stats: %d snapshots, total size %s", agg.SnapshotCount, agg.TotalSize)
 	return agg
 }
 
@@ -932,6 +935,7 @@ func (m *Manager) listAllDumpFiles() []DumpFileInfo {
 			}
 		}
 	}
+	m.logger.Printf("[INFO] [backup] Found %d DB dump files across drives", len(allFiles))
 	return allFiles
 }
 
@@ -979,7 +983,9 @@ func (m *Manager) saveSnapshotHistory() {
 	}
 	if err := os.Rename(tmp, m.snapshotHistoryFile); err != nil {
 		m.logger.Printf("[WARN] Could not rename snapshot history file: %v", err)
+		return
 	}
+	m.logger.Printf("[INFO] [backup] Saved snapshot history (%d entries)", len(m.snapshotHistory))
 }
 
 // loadSnapshotHistoryFromFile reads the persisted snapshot history from disk.