Move web-only agentic and classic chat components from duo-ui package to gitlab application
## Problem to solve
Web-only agentic and classic chat components are currently distributed across the duo-ui package and the gitlab application project. This split creates friction in the development workflow and adds unnecessary complexity when working on Duo Chat features.
Files in in duo-ui:
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/chat/web_duo_chat.vue
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/chat/web_duo_chat.scss
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/chat/web_duo_chat.spec.js
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/agentic_chat/web_agentic_duo_chat.vue
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/agentic_chat/web_agentic_duo_chat.spec.js
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/chat/components/duo_chat_header/web_duo_chat_header.vue
* https://gitlab.com/gitlab-org/duo-ui/-/blob/main/src/components/chat/components/duo_chat_header/web_duo_chat_header.spec.js
## Solution proposal
Move web-only agentic and classic chat components from the duo-ui package (gitlab-org/duo-ui) to the gitlab application project (gitlab-org/gitlab) consolidating all related source code in a single repository.
## Reasoning
Consolidating source code in a single repository will make the Duo Chat development workflow more effective by:
- Eliminating the need to coordinate changes across multiple repositories.
- Simplifying the development setup and reducing context switching.
- Making it easier to test and iterate on chat features.
- Reducing build and deployment complexity.
- Improving code discoverability for developers working on Duo Chat.
## Tasks
- [ ] Expose `web_agentic_duo_chat.vue` and `web_duo_chat_header.vue` internal dependencies as part of the duo-ui package API.
- [ ] Move `web_agentic_duo_chat.vue` to the `gitlab-org/gitlab` project and rename it to `duo_agentic_chat_view.vue`.
- [ ] Move `web_duo_chat.vue` to the `gitlab-org/gitlab` project and rename it to `duo_chat_view.vue`.
- [ ] Move `web_duo_chat_header.vue` to the `gitlab-org/gitlab` project and rename it to `duo_chat_header.vue`.
- [ ] Rename `duo_agentic_chat.vue` component located in `gitlab-org/gitlab` project to `agentic_duo_chat_state_manager.vue`
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