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.

packaging/client/README.md

@@ -2,10 +2,10 @@
 
 Single-container deploy that runs Numa as an ODoH (RFC 9230) client: every
 DNS query routes through an independent relay + target so neither operator
-sees both your IP and your question. See the [ODoH integration doc][odoh]
-for the full protocol and privacy trade-offs.
+sees both your IP and your question. See the [ODoH upstream recipe][odoh]
+for the protocol details and the bootstrap-pinning trade-offs.
 
-[odoh]: ../../docs/implementation/odoh-integration.md
+[odoh]: ../../recipes/odoh-upstream.md
 
 ## Prerequisites