fix: fix lazy associations, LazyInitalizationErrros, address OSIV tech-debt

[balazs-szucs]

📝 Description

NOTE: this is almost straight from my PR to former BL upstream. Most of the works has been done in January, original PR submitted in February, and since then I have been running these changes on my private fork.

The port to grimmory, is strictly WIP. Better PR message is to after follow this.

Linked Issue: Fixes #

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🏷️ Type of Change

• Bug fix
• New feature
• Enhancement to existing feature
• Refactor (no behavior change)
• Breaking change (existing functionality affected)
• Documentation update

🔧 Changes

🧪 Testing (MANDATORY)

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Manual testing steps you performed:

Regression testing:

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Test output:

Backend test output (./gradlew test)

PASTE OUTPUT HERE

Frontend test output (ng test)

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📸 Screen Recording / Screenshots (MANDATORY)

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✅ Pre-Submission Checklist

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• This PR is linked to an approved issue
• Code follows project backend and frontend conventions
• Branch is up to date with develop (merge conflicts resolved)
• I ran the full stack locally (backend + frontend + database) and verified the change works
• Automated tests added or updated to cover changes (backend and frontend)
• All tests pass locally and output is pasted above
• Screen recording or screenshots are attached above proving the change works
• PR is a single focused change (one bug fix OR one feature, not multiple unrelated changes)
• PR is reasonably scoped (PRs over 1000+ changed lines will be closed, split into smaller PRs)
• No unsolicited refactors, cleanups, or "improvements" are bundled in
• Flyway migration versioning is correct (if schema was modified)
• Documentation PR submitted to booklore-docs (if user-facing changes)

🤖 AI-Assisted Contributions

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• I have read and understand every line of this PR and can explain any part of it during review
• I personally ran the code and verified it works (not just trusted the AI's output)
• PR is scoped to a single logical change, not a dump of everything the AI suggested
• Tests validate actual behavior, not just coverage (AI-generated tests often assert nothing meaningful)
• No dead code, placeholder comments, TODOs, or unused scaffolding left behind by AI
• I did not submit refactors, style changes, or "improvements" the AI suggested beyond the scope of the issue

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💬 Additional Context (optional)

Summary by CodeRabbit

• Performance Improvements

  • Faster list and shelf loading via smarter prefetching and batch loading.

• Reading Progress

  • Improved auto-progress handling: completion detection and finished-date auto-setting.
  • More consistent default read status for accurate tracking.

• Audio Metadata

  • More reliable audiobook metadata extraction (duration, chapters, cover art).

• Chores

  • Wider transactional and data-loading consistency for more reliable operations.