fix: reject whitespace and control characters in base URLs and warn on plain http Gitea (SEC-10)

docs/security.md

@@ -177,7 +177,10 @@ confirmation, `READ_ONLY`, `TOOLSETS`, `DISABLED_TOOLS` and narrow token scopes
   MCP path and the unauthenticated OAuth paths (`/register`, `/authorize`, `/token`, `/revoke`,
   consent, callback), before authentication. Client IPs come from `X-Forwarded-For` only for
   `FORWARDED_ALLOW_IPS`; a forwarded header from any other peer is ignored and logged once.
-- `PUBLIC_BASE_URL` must be https unless loopback. Gitea redirects are never followed.
+- `PUBLIC_BASE_URL` must be https unless loopback. `GITEA_URL` and `PUBLIC_BASE_URL` reject
+  whitespace, backslashes and control characters and are rebuilt from their parsed parts;
+  plain http `GITEA_URL` to a non-loopback host prints a startup warning. Gitea redirects are
+  never followed.
 - stdio: stdout carries JSON-RPC only; all logging goes to stderr.
 
 ### Per-user OAuth design