ci: add dependency vulnerability scans

[Busiii-adetiba]

Summary:

• Add OWASP Dependency-Check Gradle scanning for Android dependencies with a high-severity failure threshold.
• Add SwiftPM dependency graph output and dependency review blocking for newly introduced high-severity vulnerabilities in iOS CI.

Closes #125

Validation performed:

• Parsed android-ci.yml and ios-ci.yml as YAML.
• Ran git diff --check.
• Attempted ./gradlew dependencyCheckAnalyze --dry-run; blocked locally because this container only has Java 25.0.2, while CI pins JDK 17.

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