security: upgrade rustls-webpki to fix RUSTSEC-2026-0049 (CRL validation bypass)

Cherry-picked from PR #353. Adds rustls 0.23+ and rustls-webpki 0.103.10+
as direct workspace dependencies to force resolution, plus tokio-tungstenite
and rustls-webpki git patches for transitive dep override.

Kept serenity at crates.io version (0.12) -- the 'next' branch has breaking
API changes that need a separate migration. The serenity/tinyclaw discord.rs
fixes were deferred.

Includes security audit report (2026-04-05).

Removed RUSTSEC-2026-0049 from deny.toml ignore list.

Refs #353

Author: AlexMikhalev