[api] Lower default max_connections to 5 on esp32/libretiny

With N=5 the static-RAM trade becomes net-negative at just 1 client
(the typical ESP32 deployment — just Home Assistant):

  +8 B static (5 slots × 4 B − 12 B removed vector object)
  −12 B heap (8 B header + 4 B slot) at 1 client
  = −4 B net

N=6 had breakeven at 2 clients; N=5 puts breakeven at 1 client so the
common case is pure win.

5 slots covers HA + dashboard + 1 reconnecting socket, which is all
most deployments ever use. Users needing more can bump explicitly in
YAML (schema max is 20).

host stays at 8 (no BSS-slot concern). esp8266 stays at 4, rp2040
stays at 4.

esphome/components/api/__init__.py

@@ -291,12 +291,12 @@ CONFIG_SCHEMA = cv.All(
             cv.SplitDefault(
                 CONF_MAX_CONNECTIONS,
                 esp8266=4,  # ~40KB free RAM, each connection uses ~500-1000 bytes
-                esp32=6,  # 520KB RAM — 6 is enough for HA + dashboard + a couple of spares
+                esp32=5,  # 520KB RAM — 5 slots makes the static-RAM trade true net-negative at 1 client
                 rp2040=4,  # 264KB RAM but LWIP constraints
-                bk72xx=6,  # Moderate RAM
-                rtl87xx=6,  # Moderate RAM
+                bk72xx=5,  # Moderate RAM — net-negative at 1 client
+                rtl87xx=5,  # Moderate RAM — net-negative at 1 client
                 host=8,  # Abundant resources, no BSS-slot concern
-                ln882x=6,  # Moderate RAM
+                ln882x=5,  # Moderate RAM — net-negative at 1 client
             ): cv.int_range(min=1, max=20),
             # Maximum queued send buffers per connection before dropping connection
             # Each buffer uses ~8-12 bytes overhead plus actual message size