Architecture decision records

Decisions that shape dns-rs and would be hard to reverse, with the reasons behind them. Accepted records are never rewritten; a new record supersedes an old one.

#	Decision	Status
0001	Rust, with hickory-proto and our own server loop	Accepted
0002	Replicas are stateless	Accepted
0003	Declarative TOML configuration	Accepted
0004	No DHCP server	Accepted
0005	Blocking runs before the cache, on an atomically swapped policy	Accepted
0006	Blocklist matching semantics	Accepted
0007	Bounded, fail-soft blocklist downloads	Accepted
0008	Test-driven development, enforced by CI and agents	Accepted
0009	Agent permissions are enforced outside prompts	Accepted
0010	Hot reload by polling and SIGHUP, blocking settings only	Accepted, amended by 0016
0011	Per-replica metrics with bounded labels	Accepted
0012	The API requires a bearer token	Accepted, amended by 0015
0013	The container listens on an unprivileged port	Accepted
0014	The Helm chart takes the configuration as TOML text	Accepted
0015	The API token file is reloaded	Accepted
0016	Local records	Accepted
0017	Conditional forwarding	Accepted