docs: document web_search_provider and cloud_* keys in config example

[ayobamiseun]

What

docs/config.example.toml documented 7 of the 13 config keys coworker/config.py supports. A user reading the example could not discover:

• web_search_provider — how to switch between duckduckgo (keyless default), tavily, and brave (coworker/config.py:40-41). There is also no GUI setting for this yet ([UX] No GUI settings for web search provider #51), so the config file is currently the only way to change it — and it was undocumented.
• The cloud_* family (cloud_base_url, cloud_auth_domain, cloud_client_id, cloud_audience, cloud_relay_ws_url) — needed by dev/staging/BYO-VPC deployments, and relevant to users asking how to minimize the cloud dependency (Will it be possible to skip OpenWorker cloud? #54): setting cloud_relay_ws_url = "" disables the relay. Added commented-out, since the defaults are the production values.

Also two small accuracy notes in the header: the Windows global config location (%APPDATA%\coworker\config.toml, per coworker/secrets.py:32), and that allowed_commands / auto_allow are honored from the global file only until workspace trust (per _GLOBAL_ONLY_FIELDS, coworker/config.py:80).

Before / after

Before — keys documented: model, mode, max_iterations, allowed_commands, auto_allow, host, port.

After — adds:

# Web search backend: "duckduckgo" (keyless, default) | "tavily" | "brave"
# (the latter two need an API key, set in the app's Settings or secret store).
web_search_provider = "duckduckgo"

# OpenWorker Cloud (sign-in + managed connectors + Slack/GitHub relay).
# Defaults point at production so a fresh install works out of the box; only
# dev/staging/BYO-VPC deployments need to change these.
#cloud_base_url = "https://api.openworker.com"
#cloud_auth_domain = "opencoworker.us.auth0.com"
#cloud_client_id = "g1l4Q1lhYWmyS03qPSf4KEJGrgq02Qam"
#cloud_audience = "https://api.opencoworker.app"
# Managed relay WebSocket endpoint (Slack/GitHub inbound). Set to "" to disable
# the relay entirely (manual Socket Mode still works).
#cloud_relay_ws_url = "wss://l4z1paxb83.execute-api.us-east-1.amazonaws.com/ocw-connect"

Verification

• The example parses with tomllib.
• Every uncommented key and every commented cloud_* name checked against coworker.config._FIELDS — no unknown keys.
• Docs-only change; no screenshots (no UI touched).