fix(bash): input redirections on compound commands

[chaliy]

Summary

• while read ... done < file and done <<< string and done << EOF now work
• Parser's parse_trailing_redirects handles HereString/HereDoc/HereDocStrip tokens
• Interpreter processes input redirects before compound execution, setting pipeline_stdin
• Preserves existing pipe-based pipeline_stdin when no input redirects present

Test plan

• 5 new tests: while read < file, herestring, heredoc, sum, for output redirect
• Existing pipe-to-while tests still pass (regression check)
• cargo test --all-features passes
• cargo clippy and cargo fmt clean