RetrieX EventSource + Shop Status Fix

Patch-only package.

Purpose

This patch extends the previous stream robustness fix and addresses two issues:

The chat now shows a visible reason when the Shopware shop/search API is unreachable or returns a system error.
Reference-probe failures no longer block the actual primary Shopware search request.

public/assets/js/base.js
- Uses native EventSource instead of a manually parsed fetch().body.getReader() stream.
- Starts a short-lived stream job with POST /ask-jobs, then opens GET /ask-sse/{jobId}.
src/Controller/AskSseController.php
- Adds POST /ask-jobs.
- Adds GET /ask-sse/{jobId} for native EventSource streaming.
- Keeps the old POST /ask-sse endpoint as backwards compatibility.
- Stores short-lived stream jobs under var/stream_jobs.
src/Commerce/ShopSearchService.php
- Reference-probe Store API failures are logged but no longer stop the primary search.
- The failure state is reset after a failed reference probe before the primary search starts.
- Retry without commerce history is skipped only after a real primary Store API system failure.
src/Agent/AgentRunner.php
- If the primary shop search has a Store API system failure, the chat displays: Shopsystem aktuell nicht erreichbar oder fehlerhaft. Grund: ...
- Repair search is skipped after primary Store API system failures.

Run:

bin/console cache:clear

If OPcache/PHP-FPM is active, reload PHP-FPM afterwards.