0b40f5a790
docs/ was not the documentation site; it was a grab bag of long-form design notes, wire contracts and observability guides that landed with feature PRs because their authors needed somewhere to put them. Root AGENTS.md already says long-form dev docs live in website/docs/developer-guide/; this moves the 14 living documents there (or to the matching user-guide section) so they are published, searchable and linked from the sidebar instead of being found by grep only. Developer guide: micro-compaction, gateway-session-lifecycle (was session-lifecycle), state-db-recovery, multiplexing-gateway, chronos-managed-cron-contract, relay-connector-contract, observer-hooks (was observability/README), gateway-monitoring (observability/monitoring), relay-shared-metrics, middleware, streaming-tts, billing-lifecycle. User guide: egress/network-isolation (was security/network-egress- isolation), features/kanban-multi-gateway (was kanban/multi-gateway). Each page got title/description frontmatter and a sidebar entry; repo- relative links became site links or GitHub blob URLs; two MDX brace hazards escaped. Every in-tree pointer (module docstrings, config comments, the relay conformance test's Path, the monitoring-doc test, gateway-internals, cron-internals, kanban docs, .dockerignore, AGENTS.md) now names the new location. `docusaurus build` passes with no unresolved links on the moved pages.