feat(FR-1881): enhance GitHub Copilot code review guidelines (#4965)

Resolves #4964 ([FR-1881](https://lablup.atlassian.net/browse/FR-1881))

## Changes

This PR enhances the GitHub Copilot code review guidelines by adding explicit instructions to prevent duplicate and redundant comments during code reviews.

### Key Updates

1. **What NOT to comment on** - New section with guidelines:
   - Avoid commenting on already resolved issues
   - Don't duplicate other reviewers' comments
   - Don't bundle unrelated issues in one comment

2. **Before commenting checklist** - Pre-review steps:
   - Check if issues were already addressed
   - Check if code was already fixed in recent commits
   - Check if other reviewers already mentioned the issue
   - Only comment if adding NEW value
   - Always check PR conversation history

3. **Formatting improvements** - Better document structure and readability

## Impact

- Reduces review noise and redundant feedback
- Improves reviewer efficiency
- Creates more focused and valuable code review discussions
- Helps maintain cleaner PR conversation threads

[FR-1881]: https://lablup.atlassian.net/browse/FR-1881?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: ironAiken2

.github/copilot-instructions.md

@@ -5,10 +5,12 @@ This file provides custom instructions for GitHub Copilot when reviewing code an
 ## Project Overview
 
 Backend.AI WebUI is a **hybrid web application** with two main UI frameworks:
+
 - **Lit-Element Web Components** (`/src`) - Legacy UI components using TypeScript
 - **React Components** (`/react`) - Modern UI components using React + Ant Design + Relay (GraphQL)
 
 ### Key Technologies
+
 - **Build System**: Rollup for bundling, pnpm for package management
 - **Styling**: Ant Design (React), Material Web Components (Lit)
 - **State Management**: Redux (legacy), Relay (GraphQL for React)
@@ -20,11 +22,13 @@ Backend.AI WebUI is a **hybrid web application** with two main UI frameworks:
 ### General Principles
 
 1. **Avoid Unnecessary Suggestions**
+
    - Do not suggest adding comments to code that is already self-explanatory
    - Focus on substantial issues (bugs, security vulnerabilities, performance problems)
    - Avoid stylistic nitpicks that don't affect code quality
 
 2. **Security First**
+
    - Always check for OWASP Top 10 vulnerabilities
    - Review for command injection, XSS, SQL injection risks
    - Validate user input handling and sanitization
@@ -34,9 +38,24 @@ Backend.AI WebUI is a **hybrid web application** with two main UI frameworks:
    - Use proper type inference when types are obvious
    - Leverage utility types (Pick, Omit, Partial, etc.)
 
+### What NOT to comment on
+
+1. **Do NOT comment on issues that have already been resolved** in the conversation thread
+2. **Do NOT duplicate comments** that other reviewers have already made
+3. **Do NOT bundle multiple unrelated issues** into a single review comment
+
+### Before commenting
+
+1. **Check if the issue was already addressed** in previous comments
+2. **Check if the code was already fixed** in recent commits
+3. **Check if another reviewer already mentioned** the same issue
+4. Only leave a comment if it adds **NEW value** to the review
+5. **Always check the PR conversation history** before commenting
+
 ### Architecture Awareness
 
 When reviewing code:
+
 - Recognize whether code is in `/src` (Lit-Element) or `/react` (React)
 - Understand the hybrid nature requires different patterns for each framework
 - Check that GraphQL queries use Relay conventions in React components
@@ -51,14 +70,17 @@ When reviewing code:
 ## Git Workflow
 
 ### Commit Message Format
+
 Follow conventional commit format:
+
 - `feat(JIRA-ISSUE): description` - New features or enhancements
 - `fix(JIRA-ISSUE): description` - Bug fixes
 - `refactor(JIRA-ISSUE): description` - Code refactoring
 - `style(JIRA-ISSUE): description` - Design changes without functionality changes
 - `chore(JIRA-ISSUE): description` - Maintenance tasks
 
 ### PR Guidelines
+
 - PR titles follow format: `prefix(JIRA-ISSUE-NUMBER): title`
 - PR description starts with: `Resolves #1234(FR-1234)`
 - Use **Squash merge** as default merge strategy