Add configurable sort policy for GetReadyWork (bd-147)

- Add SortPolicy type with hybrid, priority, oldest constants
- Add SortPolicy field to WorkFilter
- Implement buildOrderByClause() for SQL generation
- Add --sort flag to bd ready command
- Add comprehensive tests for all 3 sort policies
- Update RPC protocol to support sort policy
- Update documentation with sort policy examples

Enables autonomous systems like VC to use strict priority ordering
while preserving hybrid behavior for interactive use.

Amp-Thread-ID: https://ampcode.com/threads/T-9d7ea9db-8d6d-4498-9daa-48a7e104ce1f
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/ready.go

@@ -44,6 +44,13 @@ func (s *SQLiteStorage) GetReadyWork(ctx context.Context, filter types.WorkFilte
 		args = append(args, filter.Limit)
 	}
 
+	// Default to hybrid sort for backwards compatibility
+	sortPolicy := filter.SortPolicy
+	if sortPolicy == "" {
+		sortPolicy = types.SortPolicyHybrid
+	}
+	orderBySQL := buildOrderByClause(sortPolicy)
+
 	// Query with recursive CTE to propagate blocking through parent-child hierarchy
 	// Algorithm:
 	// 1. Find issues directly blocked by 'blocks' dependencies
@@ -85,23 +92,9 @@ func (s *SQLiteStorage) GetReadyWork(ctx context.Context, filter types.WorkFilte
 		AND NOT EXISTS (
 		SELECT 1 FROM blocked_transitively WHERE issue_id = i.id
 		)
-		ORDER BY 
-		  -- Hybrid sort: recent issues (48 hours) by priority, then oldest-first
-	  CASE 
-	    WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN 0
-	    ELSE 1
-	  END ASC,
-	  CASE 
-	    WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN i.priority
-	    ELSE NULL
-	  END ASC,
-	  CASE 
-	    WHEN datetime(i.created_at) < datetime('now', '-48 hours') THEN i.created_at
-	    ELSE NULL
-	  END ASC,
-	  i.created_at ASC
-	%s
-	`, whereSQL, limitSQL)
+		%s
+		%s
+	`, whereSQL, orderBySQL, limitSQL)
 
 	rows, err := s.db.QueryContext(ctx, query, args...)
 	if err != nil {
@@ -180,3 +173,32 @@ func (s *SQLiteStorage) GetBlockedIssues(ctx context.Context) ([]*types.BlockedI
 
 	return blocked, nil
 }
+
+// buildOrderByClause generates the ORDER BY clause based on sort policy
+func buildOrderByClause(policy types.SortPolicy) string {
+	switch policy {
+	case types.SortPolicyPriority:
+		return `ORDER BY i.priority ASC, i.created_at ASC`
+
+	case types.SortPolicyOldest:
+		return `ORDER BY i.created_at ASC`
+
+	case types.SortPolicyHybrid:
+		fallthrough
+	default:
+		return `ORDER BY
+			CASE
+				WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN 0
+				ELSE 1
+			END ASC,
+			CASE
+				WHEN datetime(i.created_at) >= datetime('now', '-48 hours') THEN i.priority
+				ELSE NULL
+			END ASC,
+			CASE
+				WHEN datetime(i.created_at) < datetime('now', '-48 hours') THEN i.created_at
+				ELSE NULL
+			END ASC,
+			i.created_at ASC`
+	}
+}