Auto-import from git on empty DB (bd-189)

- Add checkAndAutoImport() that detects empty DB with issues in git
- Automatically imports from git HEAD:.beads/issues.jsonl
- Integrated into list, ready, and stats commands
- Zero cognitive load for agents in fresh clones
- Makes JSONL truly the source of truth
- DB becomes ephemeral cache that auto-rebuilds

Also:
- Update AGENTS.md onboarding section with import instructions
- Merge PR #98 (enhanced .gitignore)

Amp-Thread-ID: https://ampcode.com/threads/T-ffcb5e95-e5a0-486b-a0ae-ce8bd861ab9d
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/list.go

@@ -137,10 +137,22 @@ var listCmd = &cobra.Command{
 		ctx := context.Background()
 		issues, err := store.SearchIssues(ctx, "", filter)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
-			os.Exit(1)
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
 		}
 
+	// If no issues found, check if git has issues and auto-import
+	if len(issues) == 0 {
+		if checkAndAutoImport(ctx, store) {
+			// Re-run the query after import
+			issues, err = store.SearchIssues(ctx, "", filter)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				os.Exit(1)
+			}
+		}
+	}
+
 		// Handle format flag
 		if formatStr != "" {
 			if err := outputFormattedList(ctx, store, issues, formatStr); err != nil {