Add GitHub Copilot instructions file

[Copilot]

Configures repository-specific instructions for GitHub Copilot coding agent per best practices.

Changes

• Added .github/copilot-instructions.md with repository context:
  • Multi-module Maven project structure (flow-server, flow-client, flow-data, etc.)
  • Build/test/lint commands for Java 21+ with Jakarta EE 11
  • Core architecture: StateNode/StateTree state management, JacksonCodec serialization bridge, Element DOM abstraction
  • Key patterns: always pass executeJs parameters via $0/$1 (never concatenate), test-first development, run spotless before committing
  • Frontend tooling: Vite dev mode, TypeScript/React/Lit support
  • Task guidance: suitable for incremental work, extra caution on core state management changes

The instructions mirror the existing CLAUDE.md structure, adapted for GitHub Copilot's coding agent workflow.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨Set up Copilot instructions #22632

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[sonarqubecloud]

Quality Gate passed

Issues
2393 New issues
2 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

1 281 files  ±0  1 281 suites  ±0   1h 17m 52s ⏱️ +37s
8 876 tests ±0  8 809 ✅ ±0  67 💤 ±0  0 ❌ ±0 
9 330 runs   - 4  9 252 ✅  - 5  78 💤 +1  0 ❌ ±0 

Results for commit f168d52. ± Comparison against base commit ee5139e.