Refactor: Extract reusable chat components from WikiLive

[anderskev]

Problem

All chat UI logic is currently embedded directly in WikiLive (lib/pearl_web/live/wiki_live.ex). The chat panel markup, message rendering, streaming state management, and event handling are tightly coupled to the wiki RAG Q&A use case.

We want to support future chat views that aren't restricted to a single repo wiki (e.g. cross-repo chat, general-purpose LLM chat, multi-agent conversations), so the chat components need to be extracted and made reusable.

Current State

Tightly coupled to WikiLive:

• Chat panel markup (slide-in panel, message list, input form) — inline HEEx in wiki_live.ex
• Chat assigns: ask_messages, ask_open, ask_current_input, ask_loading
• Event handlers: toggle_ask, ask, handle_info({:answer_chunk, ...}), handle_info(:answer_complete), handle_info({:answer_error, ...})
• Streaming task supervision for chunked LLM responses

Already generic / reusable:

• MarkdownComponent — renders markdown with syntax highlighting + Mermaid
• JS hooks — ScrollToBottom, AutoFocus, Highlight, Mermaid
• CSS animations for slide-in panel
• Layout "Ask" button (just toggles a flag)

Proposed Approach

1. Extract chat function components — message bubble, message list, chat input, chat panel container into a new ChatComponents module
2. Extract chat state + event handling — into a reusable module (e.g. ChatState or a LiveComponent) that any LiveView can mount and delegate to
3. Make the data source pluggable — the chat module should accept a callback/function for generating responses, rather than hard-coding Rag.ask/3
4. Keep WikiLive as a thin consumer — WikiLive wires up the reusable chat with its RAG-specific response function

Acceptance Criteria

• Chat UI components are in their own module, reusable across LiveViews
• Chat streaming state management is extractable (not wiki-specific)
• A new LiveView can add a chat panel without duplicating WikiLive's chat code
• Existing WikiLive + RAG Q&A behavior is preserved
• Tests pass