Simplify transport module and remove unnecessary complexity

[Mng-dev-ai]

Summary

• Removes 87 lines of unnecessary complexity from the transport module (90 added, 177 removed)
• Eliminates dead code, redundant abstractions, and single-use wrappers across base.py, docker.py, and host.py
• Centralizes shared logic (TERM env var, module-level logging) and simplifies expressions throughout

Changes

Removed abstractions:

• _get_logger abstract method → module-level logger in each file
• _ensure_input_open → inlined into write()
• _preexec_drop_privileges wrapper → direct partial(self._set_process_ids, ...)
• _write_stream_eof → merged into _send_eof

Simplified logic:

• _parse_json_buffer whitespace handling (4 lines → 1 line)
• first_brace_positions list comprehension (9 lines) → compiled JSON_START_RE regex (4 lines)
• servers_for_cli for-loop → dict comprehension, removed dead if servers_for_cli: guard
• _send_eof null checks (3 early returns → 1 short-circuit chain)
• _kill_exec_process Running + Pid checks combined into short-circuit
• Env setup: os.environ.copy() + update() + assignments → single dict literal with ** unpacking
• TERM env var centralized in _prepare_environment (was duplicated in both subclasses)

Removed dead code:

• isinstance(chunk, str) check (queue only contains str and sentinel)
• seen set in _resolve_run_user (duplicate lookup is harmless)
• Redundant if servers_for_cli: guard (always true for non-empty dict)
• Dead or env.get("USER", "user") fallback (_prepare_environment guarantees non-empty)

Narrowed exception handling:

• end_input: except Exception → except (OSError, CLIConnectionError)
• _send_eof in docker: except Exception → except OSError
• Removed redundant double exception wrapping in docker connect

Test plan

• Verify Docker transport connects and streams CLI output correctly
• Verify Host transport connects and streams CLI output correctly
• Verify EOF handling works for both transports
• Verify process cleanup on close for both transports