test(subgraph): cover indexing pipeline and document operations

[toxxxxicc]

Summary

• Add Matchstick coverage for mapping handlers and representative event-to-entity query data.
• Document schema entities, relationships, identifiers, and deployment/rollback procedures.
• Configure CI to run mapping tests and supply per-environment contract addresses for deployments.
• Initialize required entity fields and avoid writing records without required parent relationships.

Verification

• Tests were not run, as requested.
• git diff --check passed; editor diagnostics reported no errors in touched TypeScript files.

Closes #673
Closes #674
Closes #675
Closes #676

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