Chat component - speech to text

[ivanvpetrov]

Add a speech to text functionality to the chat component.

The actual transcription is done by one of two options:

1. (entirely on frontend) Webspeech API
   https://developer.mozilla.org/en-US/docs/Web/API/Web_Speech_API
2. (on complimentary backend) Backend handling the communication to a 3rd party provider : Google Speech/Vertex AI/etc
   https://github.com/IgniteUI/igniteui-speech-to-text-server

[kdinev]

@ivanvpetrov Please resolve the conflicts on this PR, because I want to revive it.
@rkaraivanov Let's try to get this finished, because it's been sitting for a while.

[Copilot]

Pull request overview

Adds speech-to-text (STT) support to the igc-chat input area, with two transcription backends (Web Speech API or a SignalR-based companion server), plus new styling hooks and Storybook configuration to demonstrate the feature.

Changes:

• Extends chat options/renderers with speechToText configuration and a speechToTextButton renderer, plus speakPlaceholder.
• Implements STT clients for Web Speech and backend (SignalR + MediaRecorder), and wires STT UI into igc-chat-input (mic/stop button + countdown ring).
• Updates styling, exported CSS parts, Storybook story configuration, and adds the SignalR dependency.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 19 comments.

Show a summary per file

File	Description
stories/chat.stories.ts	Demonstrates new STT options (speakPlaceholder, speechToText) and updates template story copy/button.
src/components/chat/types.ts	Adds speakPlaceholder, speechToText options type, and speechToTextButton renderer type.
src/components/chat/themes/input.base.scss	Adds STT UI animation/countdown styles.
src/components/chat/extras/stt-client-base.ts	Introduces a base STT client with silence timeout + countdown signaling.
src/components/chat/extras/stt-client-webspeech.ts	Implements Web Speech API STT client.
src/components/chat/extras/stt-client-backend.ts	Implements SignalR + MediaRecorder STT client for the companion server.
src/components/chat/chat.ts	Exposes additional forwarded parts for STT container/button.
src/components/chat/chat-input.ts	Renders/controls the STT button, placeholder switching, and transcript injection into input state.
package.json	Adds @microsoft/signalr dependency.
package-lock.json	Lockfile updates reflecting the new dependency.

[ivanvpetrov]

The PR was merged with master. All conflicts fixed.
Parts of the code was refactored after extensive copilot review.
Tests added for coverage.

@rkaraivanov The PR is ready for further review and functionality introduction.