phase 3 review: fix broken error classification, stub checks, wasted uuid, token idempotency, dead code

- actuator/ssh.go: custom errorsAs chain broken — all SSH errors classified as SSHErrorOther.
  Replaced with standard errors.As + errors.Is.
- scheduler/scheduler.go: all four check functions were stubs returning healthy.
  Implemented real HTTP GET, TCP dial, unix.Statfs disk, and TLS cert expiry checks.
- learning/learning.go: uuid.NewV7() called unconditionally before ON CONFLICT upsert.
  Now looks up existing pattern first, reuses entity_id.
- notifier/notifier.go: removed dead var_, fixed token regeneration every 15s.
  Now skips if token_hash already set.
- phase3.go: removed dead GetPattern+dummy args call in PatchPattern.
- classify.go: removed unused var_ guard.

internal/learning/learning.go

@@ -105,11 +105,26 @@ func processGroup(ctx context.Context, pool *db.Pool, q *sqlcgen.Queries,
 	// Cap by sample size: nothing looks confident before 5 samples
 	confidence = math.Min(confidence, float64(total)/5.0)
 
-	// Get or create pattern
-	patternID, _ := uuid.NewV7()
+	// Get or create pattern — first look up existing entity, then upsert.
+	existing, err := q.GetPattern(ctx, sqlcgen.GetPatternParams{
+		AppliesType: appliesType,
+		Action:      action,
+	})
+
+	var patternID uuid.UUID
+	if err == nil && existing.EntityID != uuid.Nil {
+		patternID = existing.EntityID
+	} else {
+		id, idErr := uuid.NewV7()
+		if idErr != nil {
+			slog.Error("learning: gen pattern uuid", "error", idErr)
+			return
+		}
+		patternID = id
+	}
 	patternSummary := action + " on " + appliesType
 
-	err := q.UpsertPattern(ctx, sqlcgen.UpsertPatternParams{
+	err = q.UpsertPattern(ctx, sqlcgen.UpsertPatternParams{
 		EntityID:      patternID,
 		AppliesType:   appliesType,
 		Action:        action,