Merge branch 'main' into chunk-data

Resolved 29 conflicting files. The notable decisions:

Confidence: main's tool-calling gate (RequiredProviderConfidence) and this
branch's local-RAG gate (DataConfidenceLevel) turned out to be the same rule
on the same axis, so they are now one field. Both tool results and data
sources raise it through RequireProviderConfidence(). The gate checks the
level strictly and no longer exempts providers trusted by configuration:
TrustedProviderIds is documented as applying to data-source security checks
only, and organizations set confidence through DataConfidence
.CustomConfidenceScheme instead. The security axis (DataSecurity, ERI,
IsTrustedForDataSourceSecurityChecks) is unchanged.

Provider creation: main's CreateProvider signature won (hfEndpointKind,
capabilityOverrides, no model parameter); tokenizerPath was added to it and
is set for every provider, including the new Hetzner, IONOS and LiteLLM.
Provider and EmbeddingProvider combine the record parameters, Lua parsing and
Lua serialization of both sides.

File types: main's hierarchy (ODT leaf, WORD parent, PowerPoint without the
legacy .ppt, TABULAR instead of DELIMITED_TABLE) plus this branch's
SPREADSHEET parent with ODS and the xlsm/xlsb/xla/xlam extensions, which the
runtime already reads. Both sides had added a conflicting HTML filter; the
reading family keeps the name, and the export path uses a narrow
HTML_DOCUMENT, following the existing LATEX/TEX split.

Runtime: main's file_data.rs is the base, including the prompt-injection
sanitizer and the extraction routes. Token counting and chunk segmentation
moved into take_released, so they act on the text the filter has released
rather than on text it is still holding. A failed count is logged and left
out instead of ending the extraction, because the app counts such a segment
itself.

Data sources: the participating-provider checks of this branch are kept, and
main's GetAllowedDataSources overload now builds on them. DirectChatService
resolves the launched chat's data source options before the check, so filter
and chat see the same options.

.NET and Rust both build clean; I18N regenerated to 4060 keys.

app/MindWork AI Studio/Settings/DataModel/DataApp.cs

@@ -57,6 +57,11 @@ public sealed class DataApp(Expression<Func<Data, DataApp>>? configSelection = n
     /// </summary>
     public StartPage StartPage { get; set; } = ManagedConfiguration.Register(configSelection, n => n.StartPage, StartPage.HOME);
 
+    /// <summary>
+    /// Whether an alert dialog should be shown when prompt-injection content is blocked.
+    /// </summary>
+    public bool ShowPromptInjectionAlert { get; set; } = ManagedConfiguration.Register(configSelection, n => n.ShowPromptInjectionAlert, true);
+
     /// <summary>
     /// Should the built-in introduction be visible on the home page?
     /// </summary>
@@ -148,7 +153,27 @@ public sealed class DataApp(Expression<Func<Data, DataApp>>? configSelection = n
     /// Should the user be allowed to add providers?
     /// </summary>
     public bool AllowUserToAddProvider { get; set; } = ManagedConfiguration.Register(configSelection, n => n.AllowUserToAddProvider, true);
-    
+
+    /// <summary>
+    /// Should the user be allowed to import plugin archives from disk?
+    /// </summary>
+    public bool AllowUserToImportPlugins { get; set; } = ManagedConfiguration.Register(configSelection, n => n.AllowUserToImportPlugins, true);
+
+    /// <summary>
+    /// Should the user be allowed to import configuration plugin archives from disk?
+    /// </summary>
+    /// <remarks>
+    /// This is a second gate on top of AllowUserToImportPlugins, and both must allow the import.
+    /// Configuration plugins deserve their own switch because they are far more powerful than an
+    /// assistant: they define LLM providers and data sources, and they lock settings.
+    /// </remarks>
+    public bool AllowUserToImportConfigurationPlugins { get; set; } = ManagedConfiguration.Register(configSelection, n => n.AllowUserToImportConfigurationPlugins, true);
+
+    /// <summary>
+    /// Should the user be allowed to share or export plugins as archives?
+    /// </summary>
+    public bool AllowUserToSharePlugins { get; set; } = ManagedConfiguration.Register(configSelection, n => n.AllowUserToSharePlugins, true);
+
     /// <summary>
     /// Should administration settings be visible in the UI?
     /// </summary>