[web_server] Address review: tighter socket auto-load, flash cost in the log, fallback compile test

tests/components/web_server/common-ap-fallback.yaml

@@ -0,0 +1,11 @@
+# STA with AP fallback plus local: true opts the fallback into captive AP mode; exercises
+# the runtime start (fallback branch in wifi loop) and end (on STA connect) paths.
+wifi:
+  ssid: MySSID
+  password: password1
+  ap:
+    ssid: "ESPHome-Test"
+    password: "Test1234!"
+
+web_server:
+  local: true

tests/components/web_server/test-ap-fallback.esp32-idf.yaml

@@ -0,0 +1,2 @@
+packages:
+  web_server: !include common-ap-fallback.yaml