(SP: 1) [FIX] Add netlify-plugin-bundle-env for Netlify SSR env var delivery (#427)

* perf(sessions): move heartbeat from DB writes to Redis sorted set

fix(about): update LinkedIn follower fallback to 1800

* fix(db): require explicit APP_ENV and add runtime env diagnostics

* fix(db): replace APP_ENV throw with runtime env diagnostics for Netlify debugging

* fix(deploy): inline all server env vars at build time for Netlify SSR runtime

* fix(deploy): add netlify-plugin-bundle-env to inject env vars into SSR runtime

* fix(deploy): typo fix

Author: LesiaUKR