feat: add Project Gutenberg catalog package

[sabraman]

Summary

• add a static Project Gutenberg integration package
• declare the OPDS provider through contributes.catalog.providers
• document that the package has no runtime module

Validation

• python3 ../marginalia-sdk/tools/validate_manifest.py --profile publish */manifest.json
• python3 ../marginalia-sdk/tools/build_package.py project-gutenberg-integration --profile publish --output dist --json
• git diff --check

Draft until the SDK schema support for static catalog provider contributions lands.

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Summary by CodeRabbit

Release Notes

• New Features

  • Project Gutenberg integration now available, enabling users to search and browse a catalog of public domain books via OPDS endpoints. EPUB files can be downloaded through the existing OPDS flow.

• Documentation

  • Documentation added for the Project Gutenberg integration.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5ae8e3a7-f504-4829-82b3-05823a55a3e5

📥 Commits

Reviewing files that changed from the base of the PR and between 8016d2d and 67645d9.

📒 Files selected for processing (3)

• README.md
• project-gutenberg-integration/README.md
• project-gutenberg-integration/manifest.json

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📝 Walkthrough

Walkthrough

This PR adds a complete Project Gutenberg integration example to the marginalia-examples repository. A new integration manifest declares OPDS1 catalog provider endpoints and metadata, a README documents the integration's current and planned behavior, and the root README registers the example in its examples list.

Changes

Project Gutenberg Integration Example

Layer / File(s)	Summary
Integration manifest and documentation project-gutenberg-integration/manifest.json, project-gutenberg-integration/README.md	The integration manifest specifies schema version, metadata (id, name, version, kind, execution mode), permissions, and OPDS1 catalog provider configuration with search URL templating and domain restrictions. The README documents current behavior (static execution, OPDS search via Gutenberg's endpoint, EPUB downloads) and future runtime behavior (read-only sandboxed provider, richer metadata support, deferred format additions).
Examples catalog registration README.md	The root README's "Included examples" list is updated to include the new project-gutenberg-integration entry.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A Gutenberg garden now grows in the list,
With OPDS flowers and manifests kissed,
Static today, but sandboxed tomorrow,
Project complete, with no need to borrow!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title accurately and directly describes the main change: adding a new Project Gutenberg catalog package with supporting files (README, manifest).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch package-contributions-catalog

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