refactor(libhttp): split HttpServer into modular TUs for faster incremental builds

Split the 1400-line HttpServer.cpp into 6 focused translation units by
functional area:
- HttpServer.cpp: core lifecycle, SSL init, session management, debug
- HttpServer_Listener.cpp: TCP connection acceptor
- HttpServer_Routes.cpp: route registration, matching, wildcard/query parsing
- HttpServer_Request.cpp: request dispatch, static files, CORS, HTTP I/O
- HttpServer_Ws.cpp: WS route registry, client management, broadcast APIs
- HttpServer_WsSession.cpp: per-session WS frames + bidirectional WS proxy

Add inc/us/detail/HttpServerImpl.hpp for internal shared definitions
(exception classes, full Session/Listener declarations) installed under
/usr/include/us/detail/. Update Makefile with proper dependency tracking.
Update README with Source Layout section and v3.3.0 changelog entry.

Modifying one module now only requires recompiling its corresponding .o
instead of the entire monolithic translation unit.

libhttp/README.md

@@ -46,6 +46,23 @@ Two shared libraries are produced:
 
 `libus_http.so` does **not** depend on libcurl. Link against `libus_httpclient.so` only when you need the client, and link both when you need both server and client (e.g. a proxy/gateway).
 
+### Source Layout
+
+The server implementation is split into modular source files for faster incremental builds:
+
+| Source File | Responsibility |
+|---|---|
+| `src/HttpServer.cpp` | Core lifecycle (construct/destruct/start/stop/run), SSL init, session management, debug utilities |
+| `src/HttpServer_Listener.cpp` | TCP connection acceptor (`Listener` class) |
+| `src/HttpServer_Routes.cpp` | HTTP route registration, route matching, wildcard→regex conversion, query parameter parsing |
+| `src/HttpServer_Request.cpp` | Request dispatch pipeline, static file serving, CORS preflight, Session HTTP read/write |
+| `src/HttpServer_Ws.cpp` | WebSocket route registration, client registry, broadcast/send APIs |
+| `src/HttpServer_WsSession.cpp` | Session WebSocket handling (regular WS frames + bidirectional WS proxy bridging) |
+
+Internal shared definitions (exception classes, full `Session`/`Listener` declarations) live in `inc/us/detail/HttpServerImpl.hpp` (installed to `/usr/include/us/detail/`).
+
+Modifying one module only requires recompiling its corresponding `.o` file — no need to rebuild the entire 1400-line translation unit.
+
 ## Quick Start
 
 ### HTTP + WebSocket Server
@@ -260,6 +277,7 @@ using WebSocketClientBase = HttpClient;
 
 ## Version History
 
+- **v3.3.0**: Split HttpServer into 6 modular translation units by functional area (core/lifecycle, listener, routes, request dispatch, WS management, WS session/proxy) for dramatically faster incremental builds. Added internal detail header `inc/us/detail/HttpServerImpl.hpp` for shared definitions across TU boundaries.
 - **v3.2.0**: Split into two shared libraries — `libus_http.so` (server only, no curl) and `libus_httpclient.so` (HttpClient, depends on curl). HttpClient implementation moved to `src/HttpClient.cpp`; `HttpClient.hpp` is declaration-only.
 - **v3.1.0**: Added WebSocket reverse proxy (`ws_proxy()`) with bidirectional async bridging, ws:// and wss:// backend support, handshake-time authorization callback.
 - **v3.0.0**: Merged WebSocketServer into HttpServer and WebSocketClient into HttpClient. Single-port HTTP+WebSocket support.