feat(http): implement shared HTTP client (ClientWithMiddleware + retry + Retry-After, OQ-40)

Adds SharedHttpClient wrapping ArcSwap<ClientWithMiddleware> with a
RetryTransientMiddleware + inlined RetryAfterMiddleware stack.
HttpClientConfig covers pool, timeout, retry policy, and optional CA
bundle/client cert. reload() rebuilds and swaps via ArcSwap. No env-var
reads; credential injection is per-request, not at construction.

Cargo.lock

@@ -105,9 +105,12 @@ version = "0.1.0"
 dependencies = [
  "alknet-call",
  "alknet-core",
+ "arc-swap",
  "async-trait",
  "axum",
  "futures",
+ "http",
+ "httpdate",
  "hyper",
  "openapiv3",
  "reqwest 0.13.4",
@@ -119,6 +122,7 @@ dependencies = [
  "thiserror 2.0.18",
  "tokio",
  "tracing",
+ "url",
  "uuid",
 ]
 
@@ -3244,6 +3248,7 @@ version = "0.11.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4fcb935c5bec503c2f0e306bdd3e58bb9029dcb14fa8d9ac76e3a5256ac0763e"
 dependencies = [
+ "aws-lc-rs",
  "bytes",
  "fastbloom",
  "getrandom 0.3.4",
@@ -3538,15 +3543,21 @@ dependencies = [
  "http-body",
  "http-body-util",
  "hyper",
+ "hyper-rustls",
  "hyper-util",
  "js-sys",
  "log",
  "percent-encoding",
  "pin-project-lite",
+ "quinn",
+ "rustls",
+ "rustls-pki-types",
+ "rustls-platform-verifier",
  "serde",
  "serde_json",
  "sync_wrapper",
  "tokio",
+ "tokio-rustls",
  "tokio-util",
  "tower",
  "tower-http",