PR 4a of the runtime service registry change.
- Remove addon pages (/addons/:addonId, AddonPage, addons/*) superseded by
service pages.
- Remove grafana_url/prometheus_url from backend config, compose, .env.example,
and README (URLs now live on service records; VITE_ frontend deep-link vars
retained).
- Add Services page (/services) with create/list/delete + sidebar nav, so
services are configurable in the tool itself and service pages are reachable.
- Update docs/REQUIREMENTS.md service-registry section; add CHANGELOG.md with
the breaking-upgrade note (MANAGE_ENCRYPTION_KEY required; grafana/prometheus
env vars removed; default widget seeding removed).
Verification: backend ruff clean, pytest 222 passed; frontend lint 0 errors,
build success, 70 tests passed.
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