docs: lift user-facing guides to recipes/, drop dangling docs/ refs

docs/ is gitignored; references to docs/implementation/*.md from public
source, configs, and packaging were dead links outside the maintainer
machine. Adds four recipes (README, dnsdist-front, doh-on-lan,
odoh-upstream) under top-level recipes/ and repoints existing pointers.

- numa.toml, packaging/client/{README.md,numa.toml}: point to
  recipes/odoh-upstream.md.
- src/{bootstrap_resolver,forward,serve}.rs: reference issue #122
  directly (module scope is broader than the ODoH-specific recipe).
- src/health.rs: drop the §-ref; iOS HealthInfo remains named as the
  canonical consumer.

src/health.rs

@@ -7,11 +7,10 @@
 //! Both handlers call [`HealthResponse::build`] to assemble the JSON
 //! response from `HealthMeta` + live inputs.
 //!
-//! JSON schema is documented in `docs/implementation/ios-companion-app.md`
-//! §4.2. The iOS companion app's `HealthInfo` struct is the canonical
-//! consumer; any change to this response must keep that struct decoding
-//! cleanly (all consumed fields are optional on the Swift side, but
-//! `lan_ip` is load-bearing for the pipeline).
+//! The iOS companion app's `HealthInfo` struct is the canonical consumer;
+//! any change to this response must keep that struct decoding cleanly (all
+//! consumed fields are optional on the Swift side, but `lan_ip` is
+//! load-bearing for the pipeline).
 
 use std::net::Ipv4Addr;
 use std::path::Path;