refactor(sdk)!: remove unused discoverIndexDtfsByChain

[devin-ai-integration]

Summary

Removes discoverIndexDtfsByChain / sdk.index.discoverByChain (and DiscoverIndexDtfsByChainParams) rather than just deprecating it. Its backing endpoint /discover/dtf is deprecated in reserve-api (#254) — a popularity-filtered browse view that can omit supported DTFs — and nothing consumes the wrapper.

Usage search across the repos on hand (dtf-interface, register, zapper, scout-etl): zero callers of discoverIndexDtfsByChain / discoverByChain / DiscoverIndexDtfsByChainParams outside the SDK's own exports, docs, and test. react-sdk never wrapped it. Register hits /discover/dtf by raw fetch in three SEO/logo scripts, unrelated to this SDK surface — left alone.

discoverIndexDtfs already accepts an optional chainId, so the chain-scoped case is sdk.index.discover({ chainId }) against the canonical /discover/dtfs. With the only other caller gone, fetchDiscoveryItems loses its path parameter and the DiscoveryPath union:

-function fetchDiscoveryItems(client, path: DiscoveryPath, params) {
-  return client.api.get({ path, query: { ... } });
+function fetchDiscoveryItems(client, params) {
+  return client.api.get({ path: "/discover/dtfs", query: { ... } });

The existing chain-scoped test now exercises discoverIndexDtfs(client, { chainId: 8453 }) and asserts the request URL is /discover/dtfs?chainId=8453.

Changeset is minor (breaking removal on a 0.x package), renamed to remove-discover-by-chain.md. Docs updated in apps/docs (discovery + workflows tables), docs/index-dtf/discovery-holders.md, docs/protocol/data-sources.md, and the react-sdk migration plan; oxfmt re-aligned the data-sources table columns, hence the wider diff there.

Verification: node scripts/llm-workflow/scope.mjs --base origin/main green (format:check, lint, sdk typecheck + test, bundle:check, docs:build, docs:links).

Link to Devin session: https://app.devin.ai/sessions/934d80460fb8438e90a4f1af36fa60e8
Open in Devin Desktop: https://app.devin.ai/desktop/session/934d80460fb8438e90a4f1af36fa60e8?variant=devin

[devin-ai-integration]

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