Enable errcheck linter and fix all production code warnings

- Enabled errcheck linter (previously disabled)
- Set tests: false in .golangci.yml to focus on production code
- Fixed 27 errcheck warnings using Go best practices:
  * Database resources: defer func() { _ = rows.Close() }()
  * Transaction rollbacks: defer func() { _ = tx.Rollback() }()
  * Best-effort closers: _ = store.Close(), _ = client.Close()
  * File writes: proper error checking on Close()
  * Interactive input: handle EOF gracefully
  * File ops: ignore ENOENT on os.Remove()
- All tests pass
- Closes bd-58

Amp-Thread-ID: https://ampcode.com/threads/T-57c9afd3-9adf-40c2-8be7-3e493d200361
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/init.go

@@ -178,7 +178,7 @@ if quiet {
 		// Prompt to install
 		fmt.Printf("Install git hooks now? [Y/n] ")
 		var response string
-		fmt.Scanln(&response)
+		_, _ = fmt.Scanln(&response) // ignore EOF on empty input
 		response = strings.ToLower(strings.TrimSpace(response))
 		
 		if response == "" || response == "y" || response == "yes" {