Firmware: OTA client, dual-board build (devkit/XIAO), version reporting, XIAO fixes

- version.txt + esp_app_desc_t version reporting (X-Frame-Version header);
  new ota_update.c checks the server's advertised version against the
  running one and streams+applies an update via esp_https_ota, gated by
  bootloader rollback (marks the image valid only after a full successful
  cycle, so a bad update can't brick a wall-mounted frame).
- Dual-OTA partition tables: partitions.csv (8MB dev board, 2MB slots) and
  new partitions_xiao.csv (4MB XIAO, 1.875MB slots -- the dev board's
  table doesn't fit the XIAO's flash). New build_for_board.sh gives each
  board its own build dir + generated sdkconfig via SDKCONFIG_DEFAULTS
  layering, so switching boards never clobbers the other's config.
- fetch_photo_info()/fetch_face_labels() were using the short
  reachability-check timeout even though the manage-menu path can be the
  first (cold, TLS-handshake-paying) request of a wake cycle -- switched
  to the longer fetch timeout to stop spurious ESP_ERR_HTTP_CONNECT
  failures.
- XIAO: the RF switch that selects onboard vs. external antenna
  (GPIO3/14) isn't initialized by plain ESP-IDF the way Seeed's Arduino
  package does it, leaving WiFi unable to reliably reach the antenna at
  all -- new board_antenna.c powers the switch and selects the onboard
  antenna, gated behind FRAME_XIAO_ANTENNA_INIT (on by default in
  sdkconfig.xiao). Also remaps the EPD DC/RST/BUSY pins, since the dev
  board's defaults (GPIO9/10/11) aren't physically exposed on the XIAO.

firmware/main/Kconfig.projbuild

@@ -1,5 +1,23 @@
 menu "ESPresso Frame Configuration"
 
+    config FRAME_XIAO_ANTENNA_INIT
+        bool "Select onboard antenna on Seeed XIAO ESP32-C6 (RF switch init)"
+        default n
+        help
+            The XIAO ESP32-C6 routes its antenna through an FM8625H RF
+            switch (GPIO3 = switch power enable, GPIO14 = antenna
+            select) so it can optionally use an external u.FL antenna
+            instead of the onboard ceramic one. Seeed's own Arduino
+            board package powers the switch and selects the onboard
+            antenna automatically at boot; plain ESP-IDF (what this
+            firmware uses) does not -- without this, the switch's
+            GPIOs are left floating and the radio may not reliably
+            reach the onboard antenna at all. Symptom: a softAP (or
+            STA connection) that starts successfully in the log but
+            is never actually visible/reachable over the air. Enabled
+            by default in sdkconfig.xiao; leave off for the DevKitC-1
+            dev board, which has no such switch.
+
     config ESP_AP_SSID
         string "Provisioning softAP SSID prefix"
         default "ESPRESSO"