Fix README/example_params drift: nonexistent name param, wrong rate default, service table

[rolker]

README / example_params.yaml drift found during onboarding doc verification

Source-verification for the new .agents/README.md (PR for #39) found the existing user-facing docs contradicting the code. These can misconfigure a field deployment, so tracking them for a proper docs pass:

1. remotes.<label>.name is not a real parameter — udp_bridge/README.md ("Name of the remote. Defaults to the label") and config/example_params.yaml (name: "robot_a_bridge") both document it, but on_configure never reads it; the remote's name is the remotes_list label itself (src/udp_bridge.cpp remote-parse loop).
2. Wrong rate-limit default — example_params.yaml says maximum_bytes_per_second: 0 means default 500000; the source default is 50000 B/s (Connection::default_rate_limit, include/udp_bridge/connection.h:175). 500000 is the socket receive-buffer size, likely the source of the confusion.
3. README service table incomplete/backwards — omits remove_subscribe/remove_advertise; the subscribe/advertise direction descriptions are inverted relative to the handlers (remote_subscribe = pull a remote topic to us; remote_advertise = push a local topic to the remote).
4. README parameter list omits newer parameters — drop_stale_packets, resend_giveup_warn_rate_per_s/..._error_rate_per_s, publish_queue_max_bytes, per-connection return_host/return_port, per-topic reliability/durability/history_depth.
5. README build badge placeholder — says "build unknown / update if CI exists"; CI exists as of Onboard repo with workspace standards #39.
6. Minor: src/udp_bridge_node.cpp top comment says "four service handlers" in the periodic group; the code creates six (the remove_* pair was added later).

The new .agents/README.md documents the verified behavior; this issue is for fixing the user-facing README + example YAML (and the node comment) to match.

Part of #39. Identified by the onboard-project skill's documentation-verification pass.

---

Authored-By: Claude Code Agent
Model: Claude Fable 5