feat(scripts): support detached dev startup

[AstroMen]

Motivation

• Starting the dev stack currently blocks the invoking shell, preventing use of the same terminal for other commands.
• Provide a safe background mode that preserves logs and PIDs so developers can start services from a single terminal and continue working.

Description

• Add CLI parsing to scripts/start_dev.sh for -d/--detach and -h/--help and introduce DETACH_MODE to control background behavior.
• Introduce configurable log and PID file variables (API_LOG_FILE, WEB_LOG_FILE, API_PID_FILE, WEB_PID_FILE) and redirect service output into those logs.
• Only install the trap cleanup handler in foreground mode, and in detach mode disown the child processes and write their PIDs to the PID files.
• Print follow-up commands for tailing logs and stopping background services while preserving the original foreground blocking behavior when no flag is provided.

Testing

• Ran a syntax check with bash -n scripts/start_dev.sh, which succeeded.
• Ran ./scripts/start_dev.sh --help to verify usage output, which succeeded and printed the help text.

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Codex Task