feat(apex): add APEXlang guidance

Pre-flight Checks

• I have searched existing issues and this is not a duplicate
• I understand this proposal needs maintainer approval before a PR can be opened

Problem Description

Oracle APEXlang guidance is missing from the upstream skills taxonomy. Contributors need source-backed guidance for exporting, validating, merging, and importing declarative .apx application metadata.

Proposed Contribution

I have prepared a focused implementation in my fork:

• Fork: https://github.com/palmaguer/oracle-ai-skills
• Branch: feat/106-apexlang
• Commit: 03a22aa
• Scope: apex/apexlang/, plus the APEX domain README/router updates required for correct routing
• Size: 10 files, approximately 306 added/changed lines

The proposed skill covers:

• APEXlang syntax and metadata structure
• Export and import workflows
• Offline validation with SQLcl
• SQL versus APEXlang format selection
• Merging, conflict resolution, and promotion gates
• Application, page, shared-component, data, integration, and AI metadata

APEXlang complements SQL and PL/SQL; it does not replace them.

Validation

• Relative Markdown links checked
• git diff --check passed
• APEX domain routing checked
• Official Oracle links checked
• Runtime APEX/SQLcl validation remains pending because no target environment is available locally

Maintainer Request

Please confirm that this contribution fits the current Oracle Skills scope and add status:approved (or provide requested changes). Once approved, I will open a PR from the fork branch and link it to this issue.

Affected Area

Skills

Additional Context

Lifecycle, JavaScript API, Workflow, PL/SQL API, and Generative AI guidance are intentionally excluded and will be proposed separately.