[Hard]: Add CI quality gates for frontend and subgraph workflows

### Context and Motivation

Repository currently lacks strong automated pull request checks for core quality gates.

### Architecture Proposal

Add CI workflow for frontend install/build/test.
Add CI workflow for subgraph codegen/build/test.
Configure trigger on pull requests.
Keep workflows readable and fast.
Document CI expectations in project docs.

### Cross-Repo Scope

.github
event-dappp/package.json
event-ticketinng/package.json
README.md

### Acceptance Criteria

- [ ] CI runs automatically on pull requests
- [ ] Frontend install, build, and test checks execute in CI
- [ ] Subgraph codegen, build, and test checks execute in CI
- [ ] CI usage and expected checks are documented

### Verification and Test Strategy

Open a test pull request.
Verify workflows start automatically.
Confirm all required checks complete successfully.
Confirm failed checks block merge if branch protection is enabled.

### Dependencies or Blockers

Requires GitHub Actions permissions enabled.
Optional branch protection setup for required checks.

Start with the package scripts in event-dappp/package.json and event-ticketinng/package.json, then review the existing .github directory and README.md. Add pull-request workflows covering frontend install, build, and test plus subgraph codegen, build, and test, and document the expected checks. Verify them by opening a test pull request and confirming the checks run and complete.

Written by the indexing model from the issue text.