Implement auto-import to complete automatic git sync workflow

Adds auto-import feature to complement bd-35's auto-export, completing
the automatic sync workflow for git collaboration.

**Implementation:**
- Auto-import checks if JSONL is newer than DB on command startup
- Silently imports JSONL when modification time is newer
- Skips import command itself to avoid recursion
- Can be disabled with --no-auto-import flag

**Documentation updates:**
- Updated README.md git workflow section
- Updated CLAUDE.md workflow and pro tips
- Updated bd quickstart with auto-sync section
- Updated git hooks README to clarify they're now optional

**Testing:**
- Tested auto-import by touching JSONL and running commands
- Tested auto-export with create/close operations
- Complete workflow verified working

Closes bd-33

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

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

cmd/bd/quickstart.go

@@ -84,6 +84,14 @@ var quickstartCmd = &cobra.Command{
 		fmt.Printf("    • Join with %s table for powerful queries\n", cyan("issues"))
 		fmt.Printf("    • See %s for integration patterns\n\n", cyan("EXTENDING.md"))
 
+		fmt.Printf("%s\n", bold("GIT WORKFLOW (AUTO-SYNC)"))
+		fmt.Printf("  bd automatically keeps git in sync:\n")
+		fmt.Printf("    • %s Export to JSONL after CRUD operations (5s debounce)\n", green("✓"))
+		fmt.Printf("    • %s Import from JSONL when newer than DB (after %s)\n", green("✓"), cyan("git pull"))
+		fmt.Printf("    • %s Works seamlessly across machines and team members\n", green("✓"))
+		fmt.Printf("    • No manual export/import needed!\n")
+		fmt.Printf("  Disable with: %s or %s\n\n", cyan("--no-auto-flush"), cyan("--no-auto-import"))
+
 		fmt.Printf("%s\n", green("Ready to start!"))
 		fmt.Printf("Run %s to create your first issue.\n\n", cyan("bd create \"My first issue\""))
 	},