## Issue: `relay.fire.hose.cam` missing `com.atproto.sync.listReposByCollection` endpoint

### Context

I'm using [TAP](https://github.com/bluesky-social/indigo/tree/main/cmd/tap) (from bluesky-social/indigo) to index Leaflet documents for a search service. TAP is a "synchronization and backfill tool for atproto apps."

### What TAP needs

TAP's [crawler.go](https://github.com/bluesky-social/indigo/blob/main/cmd/tap/crawler.go) uses `com.atproto.sync.listReposByCollection` to discover repos that have records in a specific collection:

```go
repoList, err := comatproto.SyncListReposByCollection(ctx, client, collection, cursor, 1000)
```

This is used when `TAP_SIGNAL_COLLECTION` is set (e.g., `pub.leaflet.document`) to enumerate only repos relevant to that collection rather than the entire network.

### The problem

`relay.fire.hose.cam` returns 404 for this endpoint:

```bash
$ curl "https://relay.fire.hose.cam/xrpc/com.atproto.sync.listReposByCollection?collection=pub.leaflet.document&limit=1"
{"error":"Not Found"}
```

The official Bluesky relay supports it:

```bash
$ curl "https://relay1.us-east.bsky.network/xrpc/com.atproto.sync.listReposByCollection?collection=pub.leaflet.document&limit=1"
{"cursor":"...","repos":[{"did":"did:plc:ukp7pzzht32uigg6bg4vxr5t"}]}
```

### Likely cause

`listReposByCollection` was [added to indigo on February 18, 2025](https://github.com/bluesky-social/indigo/commit/10fe963). `relay.fire.hose.cam` may be running an older version.

### Workaround

Switched to the official Bluesky relay: https://github.com/zzstoatzz/leaflet-search/commit/8289eb7

```toml
TAP_RELAY_URL = 'https://relay1.us-east.bsky.network'
```