fix (fastlane): use timestamp for build numbers

TestFlight API can return stale data when builds are processing,
causing race conditions with sequential numbering.

Timestamp format YYMMDDHHMM guarantees uniqueness and always
increases (e.g., 2512181805 for Dec 18, 2025 18:05 UTC).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: pythoninthegrass

fastlane/Fastfile

@@ -55,30 +55,13 @@ def get_app_version
   end
 end
 
-# Get the next unique build number for TestFlight
+# Get a unique build number using timestamp
+# This avoids race conditions with TestFlight API returning stale data
 def get_next_build_number
-  key = api_key
-  return 1 unless key
-
-  app_version = get_app_version
-  UI.message("App version from Cargo.toml: #{app_version}")
-
-  # Get latest build number from TestFlight for this version
-  begin
-    latest_build = latest_testflight_build_number(
-      api_key: key,
-      app_identifier: APP_IDENTIFIER,
-      version: app_version
-    )
-    UI.message("Latest TestFlight build number for v#{app_version}: #{latest_build}")
-  rescue => e
-    UI.message("No existing builds found for v#{app_version}, starting at 1")
-    latest_build = 0
-  end
-
-  new_build = latest_build + 1
-  UI.message("New build number: #{new_build}")
-  new_build
+  # Format: YYMMDDHHMM (fits in 32-bit integer, always increasing)
+  build_number = Time.now.utc.strftime("%y%m%d%H%M").to_i
+  UI.message("Build number (timestamp): #{build_number}")
+  build_number
 end
 
 # Update tauri.conf.json with version from Cargo.toml and unique build number