chore: add maintainer ownership, dependency and security automation

[BLCCoreStudio]

Summary

Adds a maintainer automation baseline tailored to OpenDevIndex's content-and-tooling model. Existing content issue forms, validation workflows, and publishing workflows are preserved.

Ownership and support

• CODEOWNERS for canonical knowledge, schema, taxonomy, quality, scripts, and automation surfaces
• SUPPORT.md that separates content corrections, content requests, tooling bugs, and security reports

Dependency and security maintenance

• Dependabot for Python requirements and GitHub Actions
• CodeQL for Python repository tooling
• auto-merge restricted to Dependabot SemVer patch updates

Releases

• generated release notes grouped around knowledge coverage, corrections, features, security, docs, and maintenance

Safety

No catalog, taxonomy, schema, content, or publishing behavior is modified by this PR.

Follow-up

Dependency Review is intentionally deferred until GitHub Dependency Graph is enabled for the repository.

[github-advanced-security]

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