feat: auto-protect forks from committing upstream issue database

When bd detects it's running in a fork (origin != steveyegge/beads),
automatically add .beads/issues.jsonl to .git/info/exclude.

This prevents contributors from accidentally including issue database
changes in their PRs. The exclusion is:
- Per-clone (doesn't modify tracked files
- One-time setup (checks if already excluded)
- Silent (only logs in debug mode)

Maintainers (origin = steveyegge/beads) are not affected.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
EOF
)

cmd/bd/main.go

@@ -195,6 +195,9 @@ var rootCmd = &cobra.Command{
 			actor = config.GetString("actor")
 		}
 
+		// Protect forks from accidentally committing upstream issue database
+		ensureForkProtection()
+
 		// Performance profiling setup
 		// When --profile is enabled, force direct mode to capture actual database operations
 		// rather than just RPC serialization/network overhead. This gives accurate profiles