[Hard]: Replace scaffold subgraph tests with real mapping coverage

### Context and Motivation

Current subgraph tests are scaffold-style and do not validate actual mapping behavior for core handlers.

### Architecture Proposal

Build event fixtures for main contract events.
Add mapping tests for EventCreated.
Add mapping tests for TicketPurchased and user-level updates.
Add mapping tests for SpecialOfferMinted and StakeClaimed.
Assert Event, Ticket, and User entity values in store.

### Cross-Repo Scope

event-ticketinng/src/event-ticketing.ts
event-ticketinng/tests/event-ticketing.test.ts
event-ticketinng/tests/event-ticketing-utils.ts
event-ticketinng/schema.graphql

### Acceptance Criteria

- [ ] EventCreated handler has meaningful mapping tests
- [ ] TicketPurchased handler updates are fully tested
- [ ] SpecialOfferMinted and StakeClaimed handlers are tested
- [ ] graph test passes with strong entity assertions

### Verification and Test Strategy

Run graph codegen.
Run graph build.
Run graph test and verify all added tests pass.
Confirm assertions validate expected entity fields.

### Dependencies or Blockers

Requires matchstick test environment setup.
May need schema/entity alignment before assertions.

Start with event-ticketinng/src/event-ticketing.ts and the scaffold tests in event-ticketinng/tests/event-ticketing.test.ts and event-ticketinng/tests/event-ticketing-utils.ts; review schema.graphql before defining entity assertions. Set up the Matchstick environment, then run graph codegen, graph build, and graph test. Done means the listed handlers have meaningful fixture-based tests with strong Event, Ticket, and User field assertions.

Written by the indexing model from the issue text.