feat(llm): auto-detect max images per request for LLM providers

Add binary-search probe endpoint POST /providers/{id}/probe-max-images
that discovers the per-request image limit by sending incrementally
more 1x1 JPEGs via the provider's own API. Result is cached in the
new max_images column on the provider config.

- LLMProviderConfig: add max_images: int | None
- LLMProvider (SQLAlchemy): add max_images column
- Migration ed28d34edde7: clean ADD COLUMN
- LLMProviderService: create/update/set_max_images
- POST /providers/{id}/probe-max-images: binary search + error parsing
- ProviderConfig.svelte: 'Detect' button in edit modal + HelpTooltip
- i18n (en/ru): 11 new keys for probe UI

backend/src/plugins/llm_analysis/models.py

@@ -29,6 +29,7 @@ class LLMProviderConfig(BaseModel):
     default_model: str
     is_active: bool = True
     is_multimodal: bool = False
+    max_images: int | None = None
 # #endregion LLMProviderConfig
 
 # #region ValidationStatus [TYPE Class]