[FEATURE] Bitbucket Cloud support

[danielmeppiel]

Summary

APM currently supports GitHub and Azure DevOps as package sources. Bitbucket Cloud is another widely used platform.

Scope

• Bitbucket Cloud (bitbucket.org)
• Note: Bitbucket uses workspace/repo instead of owner/repo

Implementation approach

This will be addressed via generic git URL support in #72 rather than a Bitbucket-specific API integration. Supporting https://bitbucket.org/workspace/repo.git as a dependency reference in apm.yml avoids the need for Bitbucket REST API v2 integration and handles the workspace/repo convention naturally.

dependencies:
  apm:
    - https://bitbucket.org/acme/design-standards.git

Authentication works via standard git credential helpers (SSH keys, credential managers) — no BITBUCKET_APM_TOKEN env var needed.

Parent issue

Part of #72 — Generic git URL support and optional output override