fix: harden category extraction breadcrumb parsing (#668)

## ℹ️ Description
- Link to the related issue(s): Issue #667
- Harden breadcrumb category extraction so downloads no longer fail when
the breadcrumb structure changes.

## 📋 Changes Summary
- Parse breadcrumb anchors dynamically and fall back with debug logging
when legacy selectors are needed.
- Added unit coverage for multi-anchor, single-anchor, and fallback
scenarios to keep diff coverage above 80%.
- Documented required lint/format/test steps in PR checklist; no new
dependencies.

### ⚙️ Type of Change
- [x] 🐞 Bug fix (non-breaking change which fixes an issue)
- [ ] ✨ New feature (adds new functionality without breaking existing
usage)
- [ ] 💥 Breaking change (changes that might break existing user setups,
scripts, or configurations)

## ✅ Checklist
- [x] I have reviewed my changes to ensure they meet the project's
standards.
- [x] I have tested my changes and ensured that all tests pass (`pdm run
test`).
- [x] I have formatted the code (`pdm run format`).
- [x] I have verified that linting passes (`pdm run lint`).
- [x] I have updated documentation where necessary.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Improved category extraction accuracy with enhanced breadcrumb
parsing.
* Better handling for listings with a single breadcrumb (returns stable
category identifier).
* More resilient fallback when breadcrumb data is missing or malformed.
* Safer normalization of category identifiers to avoid incorrect parsing
across site variations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/kleinanzeigen_bot/resources/translations.de.yaml

@@ -216,6 +216,10 @@ kleinanzeigen_bot/extract.py:
   _extract_contact_from_ad_page:
     "No street given in the contact.": "Keine Straße in den Kontaktdaten angegeben."
 
+  _extract_category_from_ad_page:
+    "Breadcrumb container 'vap-brdcrmb' not found; cannot extract ad category: %s": "Breadcrumb-Container 'vap-brdcrmb' nicht gefunden; kann Anzeigenkategorie nicht extrahieren: %s"
+    "Falling back to legacy breadcrumb selectors; collected ids: %s": "Weiche auf ältere Breadcrumb-Selektoren aus; gesammelte IDs: %s"
+
 #################################################
 kleinanzeigen_bot/utils/i18n.py:
 #################################################