Explorer-Flagged Subgraph Improvements

Nobody has claimed this yet.

## Context

As part of ongoing work to reduce direct RPC usage in the Livepeer Explorer, the Explorer team migrated several core data paths from contract calls to **The Graph subgraph** (see [Explorer#327](https://github.com/livepeer/explorer/issues/327)).

All remaining RPC calls in Explorer are currently **blocked on additional subgraph coverage**.

During that migration, the Explorer team identified several areas where extending the subgraph (via schema changes, mappings, or substreams) could unlock further RPC → subgraph migrations and improve Explorer performance.

Detailed findings and endpoint-level context are documented [here](https://github.com/livepeer/explorer/issues/327#issuecomment-3648650190)

## Goal

Enable the Explorer team to fully remove remaining RPC dependencies by:

* Reviewing Explorer-flagged data gaps
* Determining which data should be indexed or derived in the subgraph
* Choosing appropriate implementations (schema updates, mapping refactors, or substreams)

This issue is intentionally high-level; specific implementation details and follow-up tasks can be defined by the subgraph owner.

Start with Explorer#327 and its linked detailed comment, then review the remaining RPC data gaps described there. Determine which gaps belong in the subgraph and whether schema changes, mapping refactors, or substreams fit; done means producing concrete follow-up tasks and implementation decisions for the subgraph owner.

Written by the indexing model from the issue text.