tooling: unify dump/screenshot surface, bound TCP sends, fix beetle input + big-dump truncation

- debug_server.c: dump_ram = alias of read_ram (one request, one response,
  up to full 2 MB); screenshot = screenshot_file (24-bit BMP, optional
  "path", default psx_screenshot.bmp); vram_peek cap 64->128; read_ram hex
  encode via nibble table (was 2M snprintf calls stalling the main thread);
  send_all_blocking bounded (1 MB chunks, SO_SNDTIMEO 2s, heartbeats the
  starvation watchdog per chunk) and drops the client on send failure
  instead of letting the watchdog kill the runtime; handle_quit tags exit
  origin.
- beetle_debug_server.c: read_ram cap 64 KB->2 MB via heap+send_raw;
  dump_ram/screenshot aliases; screenshot w/h->width/height parity;
  set_input now holds until clear_input (frames param optional) matching
  psx-runtime semantics — the old default expired after 1 frame and the
  off-by-one in the getter cleared the override before it was ever read,
  so scripted beetle navigation silently did nothing; wtrace_dump response
  heap-built + send_raw (per-entry send_fmt dropped chunks on multi-MB
  responses, producing broken JSON).
- crash_trace: new psx_crash_trace_set_exit_origin(); report gains
  exit_origin (tcp_quit / sdl_window_close / unknown).
- debug_client.py: O(n) string-aware brace parser (old per-byte loop was
  O(n^2) — minutes on a 2 MB response, which starved the server's send and
  got the runtime killed); generic key=value passthrough for any server
  command without a bespoke CLI mapping.
- TCP_COMMANDS.md updated for all of the above.

Verified: 2 MB read_ram round-trip 0.75 s; scripted beetle navigation
reaches the memcard file-select; wtrace_dump returns valid JSON at 21 MB.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

runtime/src/main.cpp

@@ -965,6 +965,7 @@ static void sdl_vblank_present(void) {
     SDL_Event ev;
     while (SDL_PollEvent(&ev)) {
         if (ev.type == SDL_QUIT) {
+            psx_crash_trace_set_exit_origin("sdl_window_close");
             shutdown_runtime();
             std::exit(0);
         } else if (ev.type == SDL_CONTROLLERDEVICEADDED) {