Add mtime TOCTOU check and wildcard flag to ConfigReloadHandle (ADR-029/030)

Extract shared read_and_validate_config() with before/after mtime check
to detect mid-write config file changes. Add ReloadError enum with
FileChangedDuringRead variant. Return HTTP 409 Conflict on mtime change
from admin reload endpoint. Store cli_allow_wildcard_bind in
ConfigReloadHandle and use it in reload() validation instead of hardcoded
false. Update all ConfigReloadHandle::new() call sites.

tests/integration_test.rs

@@ -865,6 +865,7 @@ async fn test_sighup_config_reload_valid_config() {
     let reload_handle = Arc::new(reverse_proxy::config::ConfigReloadHandle::new(
         config_arc.clone(),
         static_config,
+        false,
     ));
 
     let dir = tempfile::tempdir().unwrap();
@@ -892,8 +893,8 @@ https_port = 443
 mode = "acme"
 acme_domains = ["test.local"]
 acme_cache_dir = "/tmp/acme-cache"
-acme_contact = "mailto:admin@test.local"
 acme_directory = "staging"
+acme_contact = "mailto:admin@test.local"
 
 [[listeners.sites]]
 host = "test.local"
@@ -921,6 +922,7 @@ async fn test_sighup_config_reload_invalid_config_keeps_old() {
     let reload_handle = Arc::new(reverse_proxy::config::ConfigReloadHandle::new(
         config_arc.clone(),
         static_config,
+        false,
     ));
 
     let dir = tempfile::tempdir().unwrap();