1. Unix socket permissions: 0o660 → 0o600 (owner-only access), preventing
other processes in the same group from injecting messages via the API.
2. Telegram bot token redaction: when file downloads fail, the bot token
embedded in the Telegram API URL is now replaced with [REDACTED] in
error messages to prevent token leakage in logs.
3. Startup warning for open allow_from: all platforms now log a WARN-level
message when allow_from is not configured, making it obvious that the
deployment permits all users. This surfaces the fail-open default so
operators can make an informed decision.
Ref #60