feat(boards): add Heltec Mesh Node T114

First color-display board on the site (nRF52840 + SX1262 + 1.14" 240x135
ST7789 TFT). Slotted into the Heltec block in boards.ts; Uf2DownloadFlow
maps the T114 id to the bootloader drive name (T114BOOT — verify on
real hardware).

Drive-by: the /flash page subtitle said "download UF2 files for nRF
boards" but the Waveshare RP2040-LoRa is also a UF2 target. Updated to
"nRF52840 and RP2040 boards".

src/pages/flash.astro

@@ -6,7 +6,7 @@ import Flasher from "../components/Flasher.svelte";
 <Base title="DongLoRa Flasher" description="Flash DongLoRa firmware onto your LoRa board from the browser">
   <h1 class="font-mono text-3xl font-bold mb-2">Firmware Flasher</h1>
   <p class="text-text-muted mb-8">
-    Flash DongLoRa firmware directly from your browser using Web Serial, or download UF2 files for nRF boards.
+    Flash DongLoRa firmware directly from your browser using Web Serial, or download UF2 files for nRF52840 and RP2040 boards.
   </p>
   <Flasher client:load />
 </Base>