feat(core): implement StaticConfig/DynamicConfig split with ArcSwap hot-reload

Split alknet-core configuration into StaticConfig (immutable after startup)
and DynamicConfig (hot-reloadable at runtime via ArcSwap).

- Add StaticConfig struct in config/static_config.rs with all fields per ADR-030
- Add DynamicConfig struct with AuthPolicy, ForwardingPolicy, RateLimitConfig
- Add ForwardingPolicy with allow_all()/deny_all() defaults (ADR-031)
- Add ConfigReloadHandle with reload() method for runtime config updates
- Replace Arc<ServerAuthConfig> with Arc<ArcSwap<DynamicConfig>> in ServerHandler
- Add config_reload_handle() to Server for obtaining reload handles
- Add AuthPolicy with authenticate_publickey/authenticate_certificate methods
- All existing tests pass with the new config structure
- Default DynamicConfig produces identical behavior to current code

Cargo.lock

@@ -75,6 +75,7 @@ version = "0.1.0"
 dependencies = [
  "alknet-core",
  "anyhow",
+ "arc-swap",
  "async-trait",
  "futures",
  "ipnetwork",
@@ -185,6 +186,15 @@ version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
 
+[[package]]
+name = "arc-swap"
+version = "1.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a3a1fd6f75306b68087b831f025c712524bcb19aad54e557b1129cfa0a2b207"
+dependencies = [
+ "rustversion",
+]
+
 [[package]]
 name = "asn1-rs"
 version = "0.6.2"