fix(ci): disable updater artifacts in Tauri debug builds via config override

The real root cause: createUpdaterArtifacts=true in tauri.conf.json causes even
debug builds to create .app.tar.gz updater bundles, which require a signing key.

Solution: add tauri.debug.conf.json with createUpdaterArtifacts=false and use
--config tauri.debug.conf.json in PR check builds. Tauri deep-merges config
overrides, so only this one setting is overridden. Works cross-platform.

---
Developed by Claude Sonnet 4.6

Author: houke

.github/workflows/fluxby-pr-check.yml

@@ -122,4 +122,4 @@ jobs:
 
       - name: Build Tauri app (debug)
         working-directory: apps/tauri
-        run: npx tauri build --debug
+        run: npx tauri build --debug --config tauri.debug.conf.json

apps/tauri/tauri.debug.conf.json

@@ -0,0 +1,5 @@
+{
+  "bundle": {
+    "createUpdaterArtifacts": false
+  }
+}