[cybrdude]

Fixes #807

getServer() has called app.enable('trust proxy') since the first commit. In Express that is trust proxy: true: every entry of X-Forwarded-For is trusted, so req.ip becomes the left-most entry, which is whatever the client put in the header before the request reached Cloud Run. req.hostname and req.protocol follow X-Forwarded-Host and X-Forwarded-Proto the same way. Function code that keys rate limits, allowlists, geo decisions or audit logs on req.ip therefore keys them on a client-chosen value.

Cloud Run places one proxy in front of the function and appends the address it accepted the connection from as the last X-Forwarded-For entry, so one trusted hop is the setting that yields that address (the same value GoogleCloudPlatform/nodejs-docs-samples#3583 settled on for the Cloud Run samples).

This change:

• adds a --trust-proxy flag / TRUST_PROXY environment variable (FrameworkOptions.trustProxy) that accepts a hop count, true, false, or a comma-separated list of trusted addresses or subnets, and passes it to Express as the trust proxy setting;
• defaults it to 1;
• documents the option in the README options table, including when to raise it (another proxy or load balancer in front of Cloud Run).

Behavior change: deployments behind an additional proxy layer that relied on true to reach the left-most entry now see the last entry; they can set TRUST_PROXY=2 (or a hop count matching their topology) or TRUST_PROXY=true to keep the previous behavior.

Tests: test/options.ts covers the default, CLI-over-env precedence, an address list and false; test/integration/http.ts adds a proxy headers block asserting that with the default only the platform-added entry is reported, and that trustProxy: true reproduces the old behavior. npm run build, npx mocha build/test --recursive (111 passing) and gts check are clean on Node 22.