fix: JSON API Pagination for >25 Ads (#797)

## ℹ️ Description
*Provide a concise summary of the changes introduced in this pull
request.*

- Link to the related issue(s): Closes #789 (completes the fix started
in #793)
- **Motivation**: Fix JSON API pagination for accounts with >25 ads.
Aligns pagination logic with weidi’s approach (starts at page 1), while
hardening error handling and tests. Based on
https://github.com/weidi/kleinanzeigen-bot/pull/1.

## 📋 Changes Summary

- Added pagination helper to fetch all published ads and use it in
delete/extend/publish/update flows
- Added robust handling for malformed JSON payloads and unexpected ads
types (with translated warnings)
- Improved sell_directly extraction with pagination, bounds checks, and
shared coercion helper
- Added/updated tests for pagination and edge cases; updated assertions
to pytest.fail style

### ⚙️ Type of Change
Select the type(s) of change(s) included in this pull request:
- [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
Before requesting a review, confirm the following:
- [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:cov:unified`).
- [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

* **New Features**
* Reliable multi-page fetching for published ads and buy-now eligibility
checks.

* **Bug Fixes**
* Safer pagination with per-page JSON handling, limits and improved
termination diagnostics; ensures pageNum is used when needed.

* **Tests**
* New comprehensive pagination tests and updates to existing tests to
reflect multi-page behavior.

* **Chores**
* Added a utility to safely coerce page numbers; minor utility signature
cleanup.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/kleinanzeigen_bot/resources/translations.de.yaml

@@ -31,6 +31,18 @@ kleinanzeigen_bot/__init__.py:
     "App version: %s": "App Version: %s"
     "Python version: %s": "Python Version: %s"
 
+  _fetch_published_ads:
+    "Empty JSON response content on page %s": "Leerer JSON-Antwortinhalt auf Seite %s"
+    "Failed to parse JSON response on page %s: %s (content: %s)": "Fehler beim Parsen der JSON-Antwort auf Seite %s: %s (Inhalt: %s)"
+    "Stopping pagination after %s pages to avoid infinite loop": "Stoppe die Seitenaufschaltung nach %s Seiten, um eine Endlosschleife zu vermeiden"
+    "Pagination request timed out on page %s: %s": "Zeitueberschreitung bei der Seitenabfrage auf Seite %s: %s"
+    "Unexpected JSON payload on page %s (content: %s)": "Unerwartete JSON-Antwort auf Seite %s (Inhalt: %s)"
+    "Unexpected 'ads' type on page %s: %s value: %s": "Unerwarteter 'ads'-Typ auf Seite %s: %s Wert: %s"
+    "Reached last page %s of %s, stopping pagination": "Letzte Seite %s von %s erreicht, beende Paginierung"
+    "No ads found on page %s, stopping pagination": "Keine Anzeigen auf Seite %s gefunden, beende Paginierung"
+    "Invalid 'next' page value in paging info: %s, stopping pagination": "Ungültiger 'next'-Seitenwert in Paginierungsinfo: %s, beende Paginierung"
+    "Invalid 'pageNum' in paging info: %s, stopping pagination": "Ungültiger 'pageNum'-Wert in Paginierungsinfo: %s, beende Paginierung"
+
   __check_ad_changed:
     "Hash comparison for [%s]:": "Hash-Vergleich für [%s]:"
     "    Stored hash: %s": "    Gespeicherter Hash: %s"
@@ -162,6 +174,7 @@ kleinanzeigen_bot/__init__.py:
   update_ads:
     "Processing %s/%s: '%s' from [%s]...": "Verarbeite %s/%s: '%s' von [%s]..."
     "Skipping because ad is reserved": "Überspringen, da Anzeige reserviert ist"
+    " -> SKIPPED: ad '%s' (ID: %s) not found in published ads": " -> ÜBERSPRUNGEN: Anzeige '%s' (ID: %s) nicht in veröffentlichten Anzeigen gefunden"
     "DONE: updated %s": "FERTIG: %s aktualisiert"
     "ad": "Anzeige"
 
@@ -299,6 +312,9 @@ kleinanzeigen_bot/extract.py:
 
   _extract_sell_directly_from_ad_page:
     "Could not extract ad ID from URL: %s": "Konnte Anzeigen-ID nicht aus der URL extrahieren: %s"
+    "Stopping pagination after %s pages to avoid infinite loop": "Stoppe die Seitenaufschaltung nach %s Seiten, um eine Endlosschleife zu vermeiden"
+    "Invalid 'next' page value in paging info: %s, stopping pagination": "Ungültiger 'next'-Seitenwert in Paginierungsinfo: %s, beende Paginierung"
+    "Invalid 'pageNum' in paging info: %s, stopping pagination": "Ungültiger 'pageNum'-Wert in Paginierungsinfo: %s, beende Paginierung"
 
 #################################################
 kleinanzeigen_bot/utils/i18n.py: