feat: PlanetScale managed-MySQL preset with setup guide and host detection (Task 3)

desktop/src/lib/dbIcons.tsx

@@ -1,4 +1,4 @@
-import { siPostgresql, siMysql, siMariadb, siSqlite, siRedis, siSupabase, siNeon } from "simple-icons";
+import { siPostgresql, siMysql, siMariadb, siSqlite, siRedis, siSupabase, siNeon, siPlanetscale } from "simple-icons";
 import type { DbType } from "./types";
 
 // Brand colors from simple-icons
@@ -64,16 +64,18 @@ export const DB_ICONS: Record<DbType, string> = {
 
 // ── Managed-PostgreSQL provider icons (Supabase, NeonDB) ──────────
 // These are NOT DbType values; connections persist as db_type="postgresql".
-type ProviderIconId = "supabase" | "neon";
+type ProviderIconId = "supabase" | "neon" | "planetscale";
 
 const PROVIDER_ICON_DATA: Record<ProviderIconId, { hex: string; path: string }> = {
   supabase: { hex: `#${siSupabase.hex}`, path: siSupabase.path },
   neon: { hex: `#${siNeon.hex}`, path: siNeon.path },
+  planetscale: { hex: `#${siPlanetscale.hex}`, path: siPlanetscale.path },
 };
 
 export const PROVIDER_LABELS: Record<ProviderIconId, string> = {
   supabase: "Supabase",
   neon: "NeonDB",
+  planetscale: "PlanetScale",
 };
 
 interface ProviderIconProps {