perf(wave1): reduce Config caps, reorder Client/Monitor for cache

Wave 1 changes:
- Reduce CFG_MAX_KEYBINDS 256→128, CFG_MAX_STRLEN 256→64, CFG_MAX_ARGS 16→8
  → saves ~2.5 MB BSS from Config struct
- Add truncation warnings to config_load when keybind/button/scroll limit reached
- Reorder Client struct: HOT fields (type, mon, tags, floating flags, geom) in first
  cache line, COLD fields (wl_listeners) at end — saves cache misses in arrange()
- Reorder LayerSurface struct similarly
- Split Monitor into Monitor/MonitorCold: hot fields (~120B) stay inline, cold layout
  state lazily allocated on first dwindle/master use
- All cold-field accesses through m->cold-> indirection
- cleanupmon frees m->cold
- Zero-warning build with clang -Werror -Wpedantic

src/ipc.c

@@ -5,6 +5,7 @@
 
 #include "client.h"
 #include "ipc.h"
+#include "layout.h"
 #include "util.h"
 
 /* IPC globals */
@@ -75,7 +76,7 @@ ipc_send_output_state(IpcOutput *ipc_out)
 	}
 
 	/* layout symbol */
-	zpeachwm_ipc_output_v2_send_layout_symbol(res, m->ltsymbol[current_tag_idx(m)]);
+	zpeachwm_ipc_output_v2_send_layout_symbol(res, m->cold->ltsymbol[current_tag_idx(m)]);
 
 	/* title/appid/fullscreen/floating */
 	if (c) {
@@ -171,10 +172,11 @@ ipc_output_handle_set_layout(struct wl_client *client,
 	if (!m || idx >= (uint32_t)layout_count) return;
 
 	int ti = current_tag_idx(m);
-	if (m->lt[ti][m->sellt[ti]] != &layouts[idx])
-		m->sellt[ti] ^= 1;
-	m->lt[ti][m->sellt[ti]] = &layouts[idx];
-	strncpy(m->ltsymbol[ti], layouts[idx].symbol, LENGTH(m->ltsymbol[ti]));
+	ensure_cold(m);
+	if (m->cold->lt[ti][m->cold->sellt[ti]] != &layouts[idx])
+		m->cold->sellt[ti] ^= 1;
+	m->cold->lt[ti][m->cold->sellt[ti]] = &layouts[idx];
+	strncpy(m->cold->ltsymbol[ti], layouts[idx].symbol, LENGTH(m->cold->ltsymbol[ti]));
 	arrange(m);
 	printstatus();
 }