refactor: split webserver.hpp (845 → 498) into routes/ws/hooks

Step 5 of the FILE_LOC_MAX ratchet. Three concern-grouped sibling
sub-headers, each included from inside the webserver class body via
the same in-class-body #include pattern used for http_request_auth.hpp
and webserver_impl_dispatch.hpp:

  webserver_routes.hpp     register_path / register_prefix /
                           register_resource (templated + shared_ptr
                           overloads), the on_* shortcuts (on_get,
                           on_post, on_put, on_delete, on_patch,
                           on_options, on_head), the table-driven
                           route() overloads, and the matching
                           unregister_path / unregister_prefix /
                           unregister_resource.

  webserver_websocket.hpp  register_ws_resource (templated +
                           shared_ptr) and unregister_ws_resource.

  webserver_hooks.hpp      add_hook (11 overloads, one per
                           hook_phase) and the
                           HTTPSERVER_COMPILATION-gated
                           make_hook_handle_ factory.

Each sub-header gates itself on SRC_HTTPSERVER_WEBSERVER_HPP_INSIDE_CLASS_,
which webserver.hpp #define's before the include block and #undef's
after, so standalone inclusion raises a #error. The headers are
installed (nobase_include_HEADERS) so consumers see the declarations
transitively through <httpserver.hpp> -> webserver.hpp -> sibling.
They are NOT added to the umbrella's sub-header list because the
inner gate forbids standalone inclusion.

Public API order is preserved verbatim. No ABI change, no semantic
change. The fully-qualified @ref tags inside webserver_hooks.hpp
(@ref httpserver::hook_phase / @ref httpserver::hook_handle ...) are
unchanged in target; only the textual form needed qualification
because doxygen parses sub-headers without the enclosing namespace
context.

FILE_LOC_MAX stays at 2700 -- webserver.cpp (2673) still pins it.
Offender list down to two files.

Verification:
  make check                          51/51 PASS (includes hygiene,
                                      install-layout, doxygen,
                                      examples, readme, release-notes)
  ./scripts/check-file-size.sh        PASS at FILE_LOC_MAX=2700

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: etr

scripts/check-file-size.sh

@@ -32,7 +32,6 @@
 # Current offenders above the long-term 500-line target (2026-05-22):
 #   src/webserver.cpp                          2673
 #   src/http_request.cpp                       1175
-#   src/httpserver/webserver.hpp                845
 #
 # FILE_LOC_MAX is pinned by the largest unfixed file (webserver.cpp at
 # 2673), so it cannot drop until the top offender is decomposed. The

src/Makefile.am

@@ -30,7 +30,7 @@ libhttpserver_la_SOURCES = string_utilities.cpp webserver.cpp http_utils.cpp fil
 # Detail headers (httpserver/detail/*.hpp) live here so they cannot leak to
 # downstream consumers — the public surface comes in through <httpserver.hpp>.
 noinst_HEADERS = httpserver/string_utilities.hpp httpserver/detail/modded_request.hpp httpserver/detail/http_endpoint.hpp httpserver/detail/body.hpp httpserver/detail/webserver_impl.hpp httpserver/detail/webserver_impl_dispatch.hpp httpserver/detail/connection_state.hpp httpserver/detail/http_request_impl.hpp httpserver/detail/route_entry.hpp httpserver/detail/lambda_resource.hpp httpserver/detail/radix_tree.hpp httpserver/detail/route_cache.hpp gettext.h
-nobase_include_HEADERS = httpserver.hpp httpserver/body_kind.hpp httpserver/constants.hpp httpserver/create_webserver.hpp httpserver/create_test_request.hpp httpserver/webserver.hpp httpserver/websocket_handler.hpp httpserver/http_utils.hpp httpserver/ip_representation.hpp httpserver/file_info.hpp httpserver/http_request.hpp httpserver/http_request_auth.hpp httpserver/http_response.hpp httpserver/http_resource.hpp httpserver/feature_unavailable.hpp httpserver/iovec_entry.hpp httpserver/http_arg_value.hpp httpserver/http_method.hpp httpserver/hook_phase.hpp httpserver/hook_action.hpp httpserver/hook_handle.hpp httpserver/hook_context.hpp
+nobase_include_HEADERS = httpserver.hpp httpserver/body_kind.hpp httpserver/constants.hpp httpserver/create_webserver.hpp httpserver/create_test_request.hpp httpserver/webserver.hpp httpserver/webserver_routes.hpp httpserver/webserver_websocket.hpp httpserver/webserver_hooks.hpp httpserver/websocket_handler.hpp httpserver/http_utils.hpp httpserver/ip_representation.hpp httpserver/file_info.hpp httpserver/http_request.hpp httpserver/http_request_auth.hpp httpserver/http_response.hpp httpserver/http_resource.hpp httpserver/feature_unavailable.hpp httpserver/iovec_entry.hpp httpserver/http_arg_value.hpp httpserver/http_method.hpp httpserver/hook_phase.hpp httpserver/hook_action.hpp httpserver/hook_handle.hpp httpserver/hook_context.hpp
 
 AM_CXXFLAGS += -fPIC -Wall