fix: wait for image upload completion before submitting ad (#716)

## ℹ️ Description
Fixes a race condition where ads were submitted before all images
finished uploading to the server, causing some images to be missing from
published ads.

- Link to the related issue(s): Issue #715
- The bot was submitting ads immediately after the last image
`send_file()` call completed, only waiting 1-2.5 seconds via
`web_sleep()`. This wasn't enough time for server-side image processing,
thumbnail generation, and DOM updates to complete, resulting in missing
images in published ads.

## 📋 Changes Summary

### Image Upload Verification (Initial Fix)
- Added thumbnail verification in `__upload_images()` method to wait for
all image thumbnails to appear in the DOM after upload
- Added configurable timeout `image_upload` to `TimeoutConfig` (default:
30s, minimum: 5s)
- Improved error messages to show expected vs actual image count when
upload times out
- Added German translations for new log messages and error messages
- Regenerated JSON schemas to include new timeout configuration

### Polling Performance & Crash Fix (Follow-up Fix)
- Fixed critical bug where `web_find_all()` would raise `TimeoutError`
when no thumbnails exist yet, causing immediate crash
- Wrapped DOM queries in `try/except TimeoutError` blocks to handle
empty results gracefully
- Changed polling to use `self._timeout("quick_dom")` (~1s with PR #718)
instead of default timeout
- Improved polling performance: reduced cycle time from ~2s to ~1.5s
- DOM queries are client-side only (no server load from frequent
polling)

**New configuration option:**
```yaml
timeouts:
  image_upload: 30.0  # Total timeout for image upload and server-side processing
  quick_dom: 1.0      # Per-poll timeout for thumbnail checks (adjustable via multiplier)
```

The bot now polls the DOM for `ul#j-pictureupload-thumbnails >
li.ui-sortable-handle` elements after uploading images, ensuring
server-side processing is complete before submitting the ad form.

### ⚙️ 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
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`).
- [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**
* Image uploads now verify completion by waiting for all uploaded
thumbnails to appear before proceeding.

* **Improvements**
  * Added a configurable image upload timeout (default 30s, minimum 5s).
* Improved timeout reporting: when thumbnails don’t appear in time, the
app returns clearer feedback showing expected vs. observed counts.

<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/__init__.py

@@ -893,7 +893,7 @@ class KleinanzeigenBot(WebScrapingMixin):
             # delete previous images because we don't know which have changed
             #############################
             img_items = await self.web_find_all(By.CSS_SELECTOR,
-                                                "ul#j-pictureupload-thumbnails > li.ui-sortable-handle")
+                                                "ul#j-pictureupload-thumbnails > li:not(.is-placeholder)")
             for element in img_items:
                 btn = await self.web_find(By.CSS_SELECTOR, "button.pictureupload-thumbnails-remove", parent = element)
                 await btn.click()
@@ -1260,6 +1260,52 @@ class KleinanzeigenBot(WebScrapingMixin):
             await image_upload.send_file(image)
             await self.web_sleep()
 
+        # Wait for all images to be processed and thumbnails to appear
+        expected_count = len(ad_cfg.images)
+        LOG.info(_(" -> waiting for %s to be processed..."), pluralize("image", ad_cfg.images))
+
+        async def check_thumbnails_uploaded() -> bool:
+            try:
+                thumbnails = await self.web_find_all(
+                    By.CSS_SELECTOR,
+                    "ul#j-pictureupload-thumbnails > li:not(.is-placeholder)",
+                    timeout = self._timeout("quick_dom")  # Fast timeout for polling
+                )
+                current_count = len(thumbnails)
+                if current_count < expected_count:
+                    LOG.debug(_(" -> %d of %d images processed"), current_count, expected_count)
+                return current_count == expected_count
+            except TimeoutError:
+                # No thumbnails found yet, continue polling
+                return False
+
+        try:
+            await self.web_await(
+                check_thumbnails_uploaded,
+                timeout = self._timeout("image_upload"),
+                timeout_error_message = _("Image upload timeout exceeded")
+            )
+        except TimeoutError as ex:
+            # Get current count for better error message
+            try:
+                thumbnails = await self.web_find_all(
+                    By.CSS_SELECTOR,
+                    "ul#j-pictureupload-thumbnails > li:not(.is-placeholder)",
+                    timeout = self._timeout("quick_dom")
+                )
+                current_count = len(thumbnails)
+            except TimeoutError:
+                # Still no thumbnails after full timeout
+                current_count = 0
+            raise TimeoutError(
+                _("Not all images were uploaded within timeout. Expected %(expected)d, found %(found)d thumbnails.") % {
+                    "expected": expected_count,
+                    "found": current_count
+                }
+            ) from ex
+
+        LOG.info(_(" -> all images uploaded successfully"))
+
     async def download_ads(self) -> None:
         """
         Determines which download mode was chosen with the arguments, and calls the specified download routine.