Fix Copilot review findings: null-safety, dash encoding, delegate mismatch

[Copilot]

Addresses the review comments left on the nullable-reference-types enablement PR: unguarded null-forgiving operators that can throw at runtime, a corrupted doc-comment character, unnecessarily nullable members, and a delegate guard/invoke mismatch.

Null-safety fixes

• Chat.stories.razor: OnBasicMessageCreated/OnTemplateMessageCreated guard against a null args.Detail instead of dereferencing it with !; Text falls back to string.Empty.
• WebViewCallback.cs: AdjustDynamicContentBatch checks the deserialized array for null before iterating, and uses ?. instead of ! when invoking on a possibly-missing target control.

Tightened nullability contracts

• DataAdapters.cs: LocalJson.From, _json, and Json are non-nullable — they're always initialized via the constructor, so the nullability was misleading.
• IgbTemplateContent.razor: Context reverted to non-nullable T (with a defensively-initialized backing field), matching DynamicContentInfo<T>.UpdateContext's existing non-null assumption. DynamicContentHolder.cs updated accordingly.

Bug fix

• RuntimeHelper.cs: SendUnmarshalledColumnDataIntentsMessage was checking _callSendUnmarshalledColumnMessage but invoking the different _callSendUnmarshalledColumnDataIntentMessage delegate. Now guards on the delegate it actually calls.

Cosmetic

• IconButton.cs: Replaced corrupted replacement-character bytes (�) in an XML doc comment with proper en-dash (–) characters.

[Copilot]

Pull request overview

This PR updates the Ignite UI for Blazor library (and its Blazing Story demos) to address prior review findings around nullable reference types: removing unsafe null-forgiving dereferences, tightening nullability contracts where values are always initialized, fixing a delegate guard/invoke mismatch in JS interop, and correcting a corrupted XML-doc character.

Changes:

• Hardened null-safety in chat story handlers and dynamic-content batch processing to avoid runtime NullReferenceExceptions.
• Tightened nullability contracts for LocalJson and IgbTemplateContent<T>.Context to match actual initialization/usage assumptions.
• Fixed RuntimeHelper.SendUnmarshalledColumnDataIntentsMessage to guard the delegate it actually invokes, and corrected an XML doc en-dash.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
stories/Components/Stories/Chat.stories.razor	Adds null guards for args.Detail and safe Text fallback when building agent replies.
src/componentsBase/WebViewCallback.cs	Adds a null-check for the deserialized batch array and avoids null-forgiving invocation when locating target controls.
src/componentsBase/RuntimeHelper.cs	Fixes delegate guard/invoke mismatch for unmarshalled “data intents” calls.
src/componentsBase/IgbTemplateContent.razor	Makes Context non-nullable and removes null-forgiving usage in template rendering.
src/componentsBase/DynamicContentHolder.cs	Updates assignment to IgbTemplateContent<T>.Context to align with non-nullable Context.
src/componentsBase/DataAdapters.cs	Makes LocalJson.From, backing field, and Json property non-nullable and removes unnecessary null-forgiving.
src/components/Blazor/IconButton.cs	Replaces corrupted XML-doc characters with a proper en-dash.

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