Some client API endpoints (e.g. keys/upload) are backed by Synapse stream writers and
should not rely on broad worker regexes or route-order fallthrough for correctness.

When explicit per-stream routing is missing, requests may be captured by generic, room, or client_reader workers, instead of:
- going to the configured stream writer
- or to `main` when that stream writer is not enabled

This refactors synapse-reverse-proxy-companion's routing so that web-facing stream-backed endpoint families
are handled explicitly and early, with deterministic writer-or-main fallback.

Add first-class support for the missing `device_lists` stream writer,
generalize the same routing model to `push_rules`,
and remove stale broad-route ownership for device-list-sensitive endpoints.