refactor: rename route_tier_kind::pattern to ::regex

The pattern tier is the regex tier everywhere else in the code
(regex_routes_, the compiled std::regex, the "regex tier" prose). Unify
the enum member with that vocabulary so the three tiers read
exact / radix / regex. Pure rename; no behavior change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: etr

src/detail/webserver_register.cpp

@@ -186,7 +186,7 @@ void webserver_impl::reject_duplicate_v2_entry_(
             throw_duplicate_registration(key);
         }
         break;
-    case route_tier_kind::pattern:
+    case route_tier_kind::regex:
         for (const auto& rr : regex_routes_) {
             if (rr.url_complete == key) throw_duplicate_registration(key);
         }
@@ -228,7 +228,7 @@ void webserver_impl::register_v2_route(const detail::http_endpoint& idx,
         param_and_prefix_routes_.insert(idx.get_url_complete(), std::move(entry),
                                         /*is_prefix=*/false);
         break;
-    case route_tier_kind::pattern:
+    case route_tier_kind::regex:
         regex_routes_.push_back(
             {idx.get_url_complete(), std::move(*tier.re), std::move(entry)});
         break;

src/detail/webserver_routes_upsert.cpp

@@ -306,7 +306,7 @@ void webserver_impl::insert_fresh_v2_entry(const detail::http_endpoint& idx,
         exact_routes_.emplace(idx.get_url_complete(),
                               make_non_prefix_entry(methods, std::move(shim)));
         break;
-    case route_tier_kind::pattern:
+    case route_tier_kind::regex:
         // Regex-tier routes do not conflict with prefix routes because
         // a literal pattern with regex metacharacters is its own key
         // (it never matches as a prefix lookup target).

src/httpserver/detail/route_tier.hpp

@@ -58,13 +58,14 @@ namespace detail {
 //
 // Inline so both webserver_register.cpp and webserver_routes.cpp can call
 // it without picking up a TU boundary.
-// 'pattern' names the regex tier; the label is self-describing:
-// routes in this tier match by compiled regex pattern.
-enum class route_tier_kind { exact, radix, pattern };
+// 'regex' names the regex tier; routes in this tier match by compiled
+// regex pattern (as opposed to the exact hash tier and the radix
+// parameterized-path tier).
+enum class route_tier_kind { exact, radix, regex };
 
 struct route_tier_result {
     route_tier_kind kind = route_tier_kind::exact;
-    std::optional<std::regex> re;  // populated iff kind == pattern
+    std::optional<std::regex> re;  // populated iff kind == regex
 };
 
 inline route_tier_result classify_route_tier(const detail::http_endpoint& idx) {
@@ -102,7 +103,7 @@ inline route_tier_result classify_route_tier(const detail::http_endpoint& idx) {
         if (std::regex_match(idx.get_url_complete(), re)) {
             res.kind = route_tier_kind::exact;
         } else {
-            res.kind = route_tier_kind::pattern;
+            res.kind = route_tier_kind::regex;
             res.re   = std::move(re);
         }
         return res;