Add migration inspection tools for AI agents (bd-627d Phase 2)

Implemented:
- bd migrate --inspect --json: Shows migration plan, db state, warnings
- bd info --schema --json: Returns schema details for agents
- Migration invariants: Validates migrations post-execution
- Added ListMigrations() for introspection

Phase 1 (invariants) and Phase 2 (inspection) complete.
Next: Wire up MCP tools in beads-mcp server.

Amp-Thread-ID: https://ampcode.com/threads/T-c4674660-d640-405f-a929-b664e8699a48
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/info.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"path/filepath"
+	"strings"
 
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/beads/internal/types"
@@ -21,11 +22,15 @@ or daemon connection. It shows:
   - Daemon connection status (daemon or direct mode)
   - If using daemon: socket path, health status, version
   - Database statistics (issue count)
+  - Schema information (with --schema flag)
 
 Examples:
   bd info
-  bd info --json`,
+  bd info --json
+  bd info --schema --json`,
 	Run: func(cmd *cobra.Command, args []string) {
+		schemaFlag, _ := cmd.Flags().GetBool("schema")
+
 		// Get database path (absolute)
 		absDBPath, err := filepath.Abs(dbPath)
 		if err != nil {
@@ -81,6 +86,55 @@ Examples:
 			}
 		}
 
+		// Add schema information if requested
+		if schemaFlag && store != nil {
+			ctx := context.Background()
+			
+			// Get schema version
+			schemaVersion, err := store.GetMetadata(ctx, "bd_version")
+			if err != nil {
+				schemaVersion = "unknown"
+			}
+			
+			// Get tables
+			tables := []string{"issues", "dependencies", "labels", "config", "metadata"}
+			
+			// Get config
+			configMap := make(map[string]string)
+			prefix, _ := store.GetConfig(ctx, "issue_prefix")
+			if prefix != "" {
+				configMap["issue_prefix"] = prefix
+			}
+			
+			// Get sample issue IDs
+			filter := types.IssueFilter{}
+			issues, err := store.SearchIssues(ctx, "", filter)
+			sampleIDs := []string{}
+			detectedPrefix := ""
+			if err == nil && len(issues) > 0 {
+				// Get first 3 issue IDs as samples
+				maxSamples := 3
+				if len(issues) < maxSamples {
+					maxSamples = len(issues)
+				}
+				for i := 0; i < maxSamples; i++ {
+					sampleIDs = append(sampleIDs, issues[i].ID)
+				}
+				// Detect prefix from first issue
+				if len(issues) > 0 {
+					detectedPrefix = extractPrefix(issues[0].ID)
+				}
+			}
+			
+			info["schema"] = map[string]interface{}{
+				"tables":          tables,
+				"schema_version":  schemaVersion,
+				"config":          configMap,
+				"sample_issue_ids": sampleIDs,
+				"detected_prefix": detectedPrefix,
+			}
+		}
+
 		// JSON output
 		if jsonOutput {
 			outputJSON(info)
@@ -125,10 +179,38 @@ Examples:
 			fmt.Printf("\nIssue Count: %d\n", count)
 		}
 
+		// Show schema information if requested
+		if schemaFlag {
+			if schemaInfo, ok := info["schema"].(map[string]interface{}); ok {
+				fmt.Println("\nSchema Information:")
+				fmt.Printf("  Tables: %v\n", schemaInfo["tables"])
+				if version, ok := schemaInfo["schema_version"].(string); ok {
+					fmt.Printf("  Schema Version: %s\n", version)
+				}
+				if prefix, ok := schemaInfo["detected_prefix"].(string); ok && prefix != "" {
+					fmt.Printf("  Detected Prefix: %s\n", prefix)
+				}
+				if samples, ok := schemaInfo["sample_issue_ids"].([]string); ok && len(samples) > 0 {
+					fmt.Printf("  Sample Issues: %v\n", samples)
+				}
+			}
+		}
+
 		fmt.Println()
 	},
 }
 
+// extractPrefix extracts the prefix from an issue ID (e.g., "bd-123" -> "bd")
+func extractPrefix(issueID string) string {
+	parts := strings.Split(issueID, "-")
+	if len(parts) > 0 {
+		return parts[0]
+	}
+	return ""
+}
+
 func init() {
+	infoCmd.Flags().Bool("schema", false, "Include schema information in output")
+	infoCmd.Flags().BoolVar(&jsonOutput, "json", false, "Output in JSON format")
 	rootCmd.AddCommand(infoCmd)
 }