feat(boards): unify homepage grid with flasher + clickable cards

Three changes, all from finally having working RAK4631 firmware and
noticing the homepage grid was hand-coded, stale, and disconnected from
the flasher.

1. RAK4631 display name. Silkscreen + RAK marketing call this module
   'RAK4631'; 'WisBlock' is the ecosystem brand. The site was showing
   'RAK WisBlock 4631', which matched neither the product name nor the
   firmware commit message ('RAK4631 WisBlock bring-up'). It also
   contradicted Uf2DownloadFlow.svelte, which already correctly told
   users 'A USB drive named RAK4631 should appear'. Renamed to 'RAK4631
   WisBlock' in boards.ts. Stable identifiers (board id, asset filename
   pattern, driveName lookup) unchanged so v1.4.0 artifacts still
   resolve.

2. Homepage grid is now data-driven from boards.ts. Previously a
   hand-coded list that had silently drifted: missing the LilyGo T-Beam
   classic, LilyGo T-Beam S3 Supreme, and the Heltec V3 UART variant.
   Now maps over the same `boards` array the flasher uses, sorted
   case-insensitively by display name. Adding a board in one place
   updates both pages. `badgeText()` and `badgeColor()` lifted out of
   BoardSelector.svelte into boards.ts so the label and accent color
   have a single source of truth too.

3. Homepage cards are now links — clicking a card takes you to
   /flash?board=<id> with that board pre-selected. Flasher.svelte reads
   the param on mount and sets selectedBoard if the id resolves, so the
   user lands on the version-picker step directly.

The flasher's BoardSelector keeps its richer UI (search filter,
MCU-family grouping) — only the simpler homepage grid was unified.

src/components/BoardSelector.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import type { BoardDef } from "../lib/types";
-  import { boards } from "../lib/boards";
+  import { boards, badgeText, badgeColor } from "../lib/boards";
 
   interface Props {
     selected: BoardDef | null;
@@ -11,28 +11,6 @@
 
   let query = $state("");
 
-  function badgeText(board: BoardDef): string {
-    switch (board.flashMethod) {
-      case "web-serial":
-        return "Web Flash";
-      case "uf2":
-        return "UF2 Download";
-      case "download-only":
-        return "CLI Only";
-    }
-  }
-
-  function badgeColor(board: BoardDef): string {
-    switch (board.flashMethod) {
-      case "web-serial":
-        return "text-accent";
-      case "uf2":
-        return "text-info";
-      case "download-only":
-        return "text-warn";
-    }
-  }
-
   function matches(board: BoardDef, q: string): boolean {
     const needle = q.trim().toLowerCase();
     if (!needle) return true;