Update gitignore files for all components

Root: add OS/IDE/secrets patterns
webapp: add .vite/, .tsbuildinfo, .env.local
backend: add /createuser binary, bin/, uploads/ (submodule bump)
app: remove redundant entries, add *.hprof, *.class

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/.gitignore

@@ -1,9 +1,7 @@
 *.iml
 .gradle/
 .idea/
-/local.properties
-/.idea/workspace.xml
-/.idea/libraries
+local.properties
 .DS_Store
 /build/
 /captures/
@@ -11,6 +9,5 @@
 .cxx/
 *.keystore
 !debug.keystore
-local.properties
-app/build/
-app/.cxx/
+*.hprof
+*.class