Fix Dependabot failing due to missing Gradle build files in /gradle directory

[Copilot]

Dependabot was configured to scan directory: "/gradle" for Gradle updates, but that directory only contains libs.versions.toml and wrapper files — no build scripts. Dependabot requires actual Gradle build files (build.gradle.kts, settings.gradle.kts) in the target directory to function.

Changes

• .github/dependabot.yml: Change directory for the version-catalog-updates group from /gradle → /

# Before
- package-ecosystem: "gradle"
  directory: "/gradle"   # No build files here — only libs.versions.toml + wrapper
  groups:
    version-catalog-updates:
      patterns:
        - "libs.versions.toml"

# After
- package-ecosystem: "gradle"
  directory: "/"         # Root contains build.gradle.kts + settings.gradle.kts
  groups:
    version-catalog-updates:
      patterns:
        - "libs.versions.toml"

Dependabot discovers gradle/libs.versions.toml automatically when scanning from /, following standard Gradle project conventions.