Search/CSRF token uses Math.random() instead of a CSPRNG

[felladrin]

Surfaced by a role-based review; verified against current code (docs/security.md already flags the weakness).

Problem: server/searchToken.ts:26 generates the token with Math.random().toString(36).substring(2) — a non-cryptographic PRNG yielding ~11 low-entropy chars. This token is the CSRF/auth gate for the SearXNG proxy and /inference.

Fix: Use crypto.randomBytes(32).toString("hex") (or crypto.randomUUID()) — a drop-in change.

Files: server/searchToken.ts