feat(webui): implement AI Copilot sidebar and resolve CORS blockers

[Makeepan-dev]

Description

I have implemented the initial frontend infrastructure and UI components for the AI Copilot feature. This PR establishes the bridge between the global navigation and the new AI-driven sidebar, while also resolving local development blockers.

#Key Changes:

AppBar Integration: Added an IconButton with the AutoAwesome icon to serve as the entry point for the AI suite.

State Management: Implemented "State Lifting" in App.tsx to synchronize the AppBar toggle with the CopilotDrawer visibility.

CopilotDrawer (New): Created a premium-styled, responsive sidebar using MUI Drawer, featuring a gradient header and a scrollable message area.

CORS Middleware Update: Modified internal/webserver/webserver.go to allow cross-origin requests, enabling the React frontend (Vite/RSPack) to communicate with the Go backend during local development.

Motivation:
To provide a seamless, modern user interface for database insights as outlined in my GSoC 2026 proposal.

AI & Automation Policy

• I am the human author and take full personal responsibility for every change in this PR.
• No AI or automated generative tool was used in any part of this PR OR I have disclosed all tool(s) below.

AI/automation tools used (leave blank if none):
Drafted architectural logic and UI component structure with the assistance of Gemini.
Used AI to refine the Material UI (MUI) styling and TypeScript definitions for better type safety.

Checklist

• Code compiles and existing tests pass locally.
• New or updated tests are included where applicable.
• Documentation is updated where applicable.
  
  
  

[Makeepan-dev]

I have completed the initial UI foundation for the AI Copilot feature. My goal with this PR was to establish a clean entry point and a "premium" feel for the assistant without disrupting the existing pgwatch3 dashboard flow.

What I’ve delivered in this PR:

Trigger UI: Added a dedicated IconButton in the AppBar using the AutoAwesome icon.

State Logic: Implemented React "State Lifting" in App.tsx to toggle the sidebar.

CopilotDrawer Component: A new, responsive MUI Drawer with a custom gradient header and a scrollable chat area.

Dev Blocker Fix: Updated internal/webserver/webserver.go to handle CORS issues, which was preventing the React frontend from talking to the Go backend on different local ports.

[pashagolub]

webui is admin. copilot must be TUI.

[Makeepan-dev]

Understood, Pavlo. Thank you for the clarification! I see that you want to keep the WebUI for admin tasks and move the Copilot to a TUI. I will pivot my GSoC proposal to focus on building a Go-based Terminal User Interface for the Copilot. I'll look into using libraries like Bubble Tea to keep it modern and interactive.