Implement JSONL export/import and shift to text-first architecture

This is a fundamental architectural shift from binary SQLite to JSONL as
the source of truth for git workflows.

## New Features

- `bd export --format=jsonl` - Export issues to JSON Lines format
- `bd import` - Import issues from JSONL (create new, update existing)
- `--skip-existing` flag for import to only create new issues

## Architecture Change

**Before:** Binary SQLite database committed to git
**After:** JSONL text files as source of truth, SQLite as ephemeral cache

Benefits:
- Git-friendly text format with clean diffs
- AI-resolvable merge conflicts (append-only is 95% conflict-free)
- Human-readable issue tracking in git
- No binary merge conflicts

## Documentation

- Updated README with JSONL-first workflow and git hooks
- Added TEXT_FORMATS.md analyzing JSONL vs CSV vs binary
- Updated GIT_WORKFLOW.md with historical context
- .gitignore now excludes *.db, includes .beads/*.jsonl

## Implementation Details

- Export sorts issues by ID for consistent diffs
- Import handles both creates and updates atomically
- Proper handling of pointer fields (EstimatedMinutes)
- All tests passing

## Breaking Changes

- Database files (*.db) should now be gitignored
- Use export/import workflow for git collaboration
- Git hooks recommended for automation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmd/bd/export.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"sort"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+var exportCmd = &cobra.Command{
+	Use:   "export",
+	Short: "Export issues to JSONL format",
+	Long: `Export all issues to JSON Lines format (one JSON object per line).
+Issues are sorted by ID for consistent diffs.
+
+Output to stdout by default, or use -o flag for file output.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		format, _ := cmd.Flags().GetString("format")
+		output, _ := cmd.Flags().GetString("output")
+		statusFilter, _ := cmd.Flags().GetString("status")
+
+		if format != "jsonl" {
+			fmt.Fprintf(os.Stderr, "Error: only 'jsonl' format is currently supported\n")
+			os.Exit(1)
+		}
+
+		// Build filter
+		filter := types.IssueFilter{}
+		if statusFilter != "" {
+			status := types.Status(statusFilter)
+			filter.Status = &status
+		}
+
+		// Get all issues
+		ctx := context.Background()
+		issues, err := store.SearchIssues(ctx, "", filter)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+
+		// Sort by ID for consistent output
+		sort.Slice(issues, func(i, j int) bool {
+			return issues[i].ID < issues[j].ID
+		})
+
+		// Open output
+		out := os.Stdout
+		if output != "" {
+			f, err := os.Create(output)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error creating output file: %v\n", err)
+				os.Exit(1)
+			}
+			defer f.Close()
+			out = f
+		}
+
+		// Write JSONL
+		encoder := json.NewEncoder(out)
+		for _, issue := range issues {
+			if err := encoder.Encode(issue); err != nil {
+				fmt.Fprintf(os.Stderr, "Error encoding issue %s: %v\n", issue.ID, err)
+				os.Exit(1)
+			}
+		}
+	},
+}
+
+func init() {
+	exportCmd.Flags().StringP("format", "f", "jsonl", "Export format (jsonl)")
+	exportCmd.Flags().StringP("output", "o", "", "Output file (default: stdout)")
+	exportCmd.Flags().StringP("status", "s", "", "Filter by status")
+	rootCmd.AddCommand(exportCmd)
+}