Add comments feature (bd-162)

- Add comments table to SQLite schema
- Add Comment type to internal/types
- Implement AddIssueComment and GetIssueComments in storage layer
- Update JSONL export/import to include comments
- Add comments to 'bd show' output
- Create 'bd comments' CLI command structure
- Fix UpdateIssueID to update comments table and defer FK checks
- Add GetIssueComments/AddIssueComment to Storage interface

Note: CLI command needs daemon RPC support (tracked in bd-163)
Amp-Thread-ID: https://ampcode.com/threads/T-ece10dd1-cf64-48ff-9adb-dd304d0bcb25
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/comments.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/user"
+
+	"github.com/spf13/cobra"
+)
+
+var commentsCmd = &cobra.Command{
+	Use:   "comments [issue-id]",
+	Short: "View or manage comments on an issue",
+	Long: `View or manage comments on an issue.
+
+Examples:
+  # List all comments on an issue
+  bd comments bd-123
+
+  # List comments in JSON format
+  bd comments bd-123 --json
+
+  # Add a comment
+  bd comments add bd-123 "This is a comment"
+
+  # Add a comment from a file
+  bd comments add bd-123 -f notes.txt`,
+	Args: cobra.MinimumNArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		issueID := args[0]
+		ctx := context.Background()
+
+		// Get comments
+		comments, err := store.GetIssueComments(ctx, issueID)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error getting comments: %v\n", err)
+			os.Exit(1)
+		}
+
+		if jsonOutput {
+			data, err := json.MarshalIndent(comments, "", "  ")
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error encoding JSON: %v\n", err)
+				os.Exit(1)
+			}
+			fmt.Println(string(data))
+			return
+		}
+
+		// Human-readable output
+		if len(comments) == 0 {
+			fmt.Printf("No comments on %s\n", issueID)
+			return
+		}
+
+		fmt.Printf("\nComments on %s:\n\n", issueID)
+		for _, comment := range comments {
+			fmt.Printf("[%s] %s at %s\n", comment.Author, comment.Text, comment.CreatedAt.Format("2006-01-02 15:04"))
+			fmt.Println()
+		}
+	},
+}
+
+var commentsAddCmd = &cobra.Command{
+	Use:   "add [issue-id] [text]",
+	Short: "Add a comment to an issue",
+	Long: `Add a comment to an issue.
+
+Examples:
+  # Add a comment
+  bd comments add bd-123 "Working on this now"
+
+  # Add a comment from a file
+  bd comments add bd-123 -f notes.txt`,
+	Args: cobra.MinimumNArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		issueID := args[0]
+
+		// Get comment text from flag or argument
+		commentText, _ := cmd.Flags().GetString("file")
+		if commentText != "" {
+			// Read from file
+			data, err := os.ReadFile(commentText)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error reading file: %v\n", err)
+				os.Exit(1)
+			}
+			commentText = string(data)
+		} else if len(args) < 2 {
+			fmt.Fprintf(os.Stderr, "Error: comment text required (use -f to read from file)\n")
+			os.Exit(1)
+		} else {
+			commentText = args[1]
+		}
+
+		// Get author from environment or system
+		author := os.Getenv("BD_AUTHOR")
+		if author == "" {
+			author = os.Getenv("USER")
+		}
+		if author == "" {
+			if u, err := user.Current(); err == nil {
+				author = u.Username
+			} else {
+				author = "unknown"
+			}
+		}
+
+		ctx := context.Background()
+
+		comment, err := store.AddIssueComment(ctx, issueID, author, commentText)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error adding comment: %v\n", err)
+			os.Exit(1)
+		}
+
+		if jsonOutput {
+			data, err := json.MarshalIndent(comment, "", "  ")
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error encoding JSON: %v\n", err)
+				os.Exit(1)
+			}
+			fmt.Println(string(data))
+			return
+		}
+
+		fmt.Printf("Comment added to %s\n", issueID)
+	},
+}
+
+func init() {
+	commentsCmd.AddCommand(commentsAddCmd)
+	commentsAddCmd.Flags().StringP("file", "f", "", "Read comment text from file")
+	rootCmd.AddCommand(commentsCmd)
+}