feat: add base chat messages

[Killusions]

Adds base chat-messages (holds content, actions and attachments), in preparation for next step (chat-container and input)

Consists of one generic chat-message (declarative) and two factories (ai and user message), as well as the attachment list.

The user-message and ai-message components are the building blocks for the chat-container.

Uses #915 (merged)

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[Copilot]

Pull Request Overview

This PR adds the foundational chat message components for building chat interfaces. The implementation includes specialized message components (user and AI), along with supporting utilities for markdown rendering, attachments, and actions.

Key changes:

• Implements comprehensive chat message system with user and AI message variants
• Adds markdown content renderer with security features and proper formatting
• Provides attachment display and management functionality with file type icons

Reviewed Changes

Copilot reviewed 62 out of 63 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
projects/element-ng/chat-messages/	Core chat message components implementation with TypeScript, tests, and styling
src/app/examples/	Example components demonstrating chat message usage patterns
docs/components/chat-messages/	Documentation updates with component examples and API references
projects/element-ng/translate/	Translation key additions for new chat message labels
projects/element-theme/src/styles/	Theme token addition for experimental input styling
playwright/	Visual regression tests and snapshots for component verification

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[github-actions]

Documentation.
Examples.
Playwright report.

Coverage Reports:

• element-ng
• element-translate-ng

[Killusions]

Added support for Markdown tables

[Killusions]

This should be ready now, I marked the base components (attachments, markdown, ...) as experimental, as we might remove or rename them or change their API.

[Killusions]

@timowolf @spike-rabbit This is also fine for UX, please have a look if you have time, then after this we can do the input and the container with #600

[spike-rabbit]

Please add some more details in the PR description.

Why do we need ai and user messages? Do they add any real value compared to the chat-message?

[Killusions]

The user-message and ai-message components are the building blocks for the chat-container, they can be used by the user using templates and ng-content, and are used internally by us.

Adjusted the description:

The user-message and ai-message components are the building blocks for the chat-container, they can be used by the user using templates and ng-content, and are also used internally by us.

[Copilot]

Pull Request Overview

Copilot reviewed 61 out of 61 changed files in this pull request and generated 4 comments.

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[timowolf]

Many thanks, some remarks here. The docs can also be changed later, but I would ask to change and remove the id of the actions and attachments if possible. I do not see any use at the moment.

[Killusions]

@timowolf Thank you, back to you

[Killusions]

axe detected an issue with the interactivity of the attachment list, fixed.

[timowolf]

❤️

[kfenner]

LGTM 👍

addressed

[github-actions]

[siemens-element-bot]

🎉 This PR is included in version 48.3.0 🎉

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