fix(app): use #if not #ifdef for the per-variant instance lock

DRAGONX_LITE_BUILD is ALWAYS defined (0 for the full node, 1 for Lite) via
$<BOOL:...>, so the previous #ifdef was true for BOTH variants — the full node
took the Lite branch and grabbed the "obsidiandragonlite" lock, so launching Lite
next still collided ("ObsidianDragonLite already running"). Switch to
#if DRAGONX_LITE_BUILD (value check), matching how the rest of the codebase
guards this macro.

Verified: full-node binary now contains only "obsidiandragon"; preprocessor check
confirms LITE=1 selects "obsidiandragonlite". (wallet_capabilities.h's #ifndef is
a separate, correct default-definition idiom — not affected.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main.cpp

@@ -441,7 +441,10 @@ static void Shutdown(SDL_Window* window, SDL_GLContext gl_context);
 
 // Global single instance lock. Keyed PER VARIANT so the full node and Lite can run side by side —
 // their config dirs are already separate (DRAGONX_APP_NAME), so only this lock kept them apart.
-#ifdef DRAGONX_LITE_BUILD
+// NB: DRAGONX_LITE_BUILD is ALWAYS defined (0 for the full node, 1 for Lite) via $<BOOL:...>, so this
+// must be #if (value), not #ifdef (existence) — #ifdef is true for both and made the full node grab
+// the Lite lock.
+#if DRAGONX_LITE_BUILD
 static dragonx::util::SingleInstance g_single_instance("obsidiandragonlite");
 #else
 static dragonx::util::SingleInstance g_single_instance("obsidiandragon");