feat(navigation): support arbitrary-depth category tree in drawer

[Plaoo]

Notes organized in nested categories can now be expanded to any depth in the navigation drawer instead of being capped at two levels. Refs #1630.

AI-assistant: Claude Code (Claude Opus 4.8)

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• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

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🟢 Metrics 33 complexity

Metric	Results
Complexity	33

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