Firmware: WiFi fast-connect cache (skip scan + DHCP on the next wake)

After a successful home-WiFi connection, caches BSSID/channel and
IP/netmask/gateway/DNS in NVS. The next wake's first connect attempt
uses the cached BSSID/channel (skips the all-channel scan) and applies
the cached IP directly once the link comes up (skips DHCP) -- a couple
fewer seconds of radio-on time per wake, free every wake since nothing
about the network actually needs renegotiating most of the time.

Falls back to a normal scan+DHCP attempt, and clears the cache, if: the
fast attempt itself fails, or it "succeeds" at the WiFi layer but the
full fetch cycle then fails anyway (a stale cached IP/DNS/gateway that
associates but can't actually reach the server). Also cleared on
(re)provisioning and factory reset, since a new network shouldn't try
to reuse the old one's cache.

The static-IP path needed care to get right without touching untested
territory: esp_netif_set_ip_info() only posts IP_EVENT_STA_GOT_IP (what
the existing connect-wait logic blocks on) once the netif is already
up, which the internal netif-glue's own WIFI_EVENT_STA_CONNECTED
handler guarantees by running first (registered earlier, in
esp_netif_create_default_wifi_sta()) -- confirmed against ESP-IDF's own
static_ip example and esp_netif_handlers.c source rather than assumed.
Falling back after a failed fast attempt also needed an explicit
esp_netif_dhcpc_start() first: esp_netif_dhcpc_stop() leaves the netif's
DHCP status STOPPED rather than resetting to INIT, and left alone the
glue would silently re-post the stale cached IP on the next connect
instead of actually running DHCP (esp_netif_action_connected).

Version bumped to 1.1.0 (real feature, not just a fix); build-verified
clean on both board configs (devkit 8MB, XIAO 4MB), no new warnings.

firmware/main/wifi_provisioning.h

@@ -2,6 +2,7 @@
 
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdint.h>
 #include "esp_err.h"
 
 #define FRAME_CFG_SSID_MAX_LEN 32
@@ -83,3 +84,38 @@ void ap_identity_get(char *ssid_out, size_t ssid_len, char *pass_out, size_t pas
  * can provision the device. Does not return.
  */
 void wifi_provisioning_start(void);
+
+/**
+ * Cached parameters from the most recent successful home-WiFi connection,
+ * letting the next wake's first connect attempt skip the all-channel scan
+ * (known BSSID/channel) and DHCP (known static IP/netmask/gateway/DNS).
+ * Fields are stored exactly as esp-wifi/esp-netif already use them
+ * internally, so they can be fed straight back in with no conversion.
+ */
+typedef struct {
+    uint8_t bssid[6];
+    uint8_t channel;
+    uint32_t ip;
+    uint32_t netmask;
+    uint32_t gateway;
+    uint32_t dns; /* 0 = none cached (best-effort; a real DHCP fallback still repopulates this) */
+} frame_wifi_cache_t;
+
+/**
+ * Loads the cached fast-connect parameters. Returns false if there's
+ * nothing cached yet, or it was invalidated (see frame_wifi_cache_clear).
+ */
+bool frame_wifi_cache_load(frame_wifi_cache_t *out);
+
+/** Saves fast-connect parameters after a successful home-WiFi connection. */
+void frame_wifi_cache_save(const frame_wifi_cache_t *cache);
+
+/**
+ * Clears the fast-connect cache. Called after a cached fast-connect
+ * attempt itself fails (BSSID/channel went stale), after a full fetch
+ * cycle fails despite a successful connection (the cached static IP may
+ * be unreachable even though the link came up), and by
+ * frame_config_save()/frame_config_clear() -- a (re)provisioning event
+ * means whatever was cached may belong to a different network entirely.
+ */
+void frame_wifi_cache_clear(void);