fix(merkle): use rails-style cid[N] query, not repeated bare cid

[niconiconi]

Bug

`freezer.{chain}.2.o.cash/api/v1/merkle?cid=6067&cid=5055&cid=7792` returns:

```
HTTP 400 Multiple values for one key: "cid"
```

The freezer service uses `serde_qs` which by default parses array values as `cid[N]=...`, not as repeated bare keys. The SDK's helper builds the latter, so every multi-cid merkle proof request fails. The frontend's `MerkleManager.ts` uses the correct bracket notation and works; only this SDK helper was the outlier.

Fix

`src/merkle/merkleClient.ts`: rename `withRepeatedQuery` → `withIndexedQuery`, output `cid%5B0%5D=6067&cid%5B1%5D=5055&cid%5B2%5D=7792`.

Tests

• `tests/merkleClient.test.ts`: regression — asserts URL contains `cid%5B0%5D=...&cid%5B1%5D=...&cid%5B2%5D=...` and does NOT match `[?&]cid=\d+&cid=\d+`.
• `tests/merkleEngine.test.ts`: existing assertion was locking in the broken format (`?cid=7`). Updated to `?cid%5B0%5D=7` plus renamed test.

124/124 tests pass.

Release

Cut as 0.1.6 once merged. SDK consumers (automation, app via SDK path) will pick up the fix on dep bump.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request updates the Merkle client to use rails-style bracket notation for query parameters (e.g., cid[0]=1) instead of repeated keys, ensuring compatibility with the server's serde_qs parser. Corresponding tests have been added and updated to verify this format. Feedback was provided to improve the robustness of the URL construction by handling cases where the base URL might already contain query parameters to avoid malformed URLs.

[gemini-code-assist]

The withIndexedQuery function unconditionally appends a ? to the URL. If the baseUrl (or the path joined to it) already contains query parameters, this will result in an invalid URL with multiple ? characters (e.g., https://api.com?key=123?cid[0]=...). While the current usage in getProofByCids might be safe with a simple base URL, making this utility more robust prevents bugs when the SDK is configured with a base URL that includes query parameters (e.g., for authentication or proxying).

Suggested change

	const withIndexedQuery = (url: string, key: string, values: Array<string | number>) => {
	const search = new URLSearchParams();
	for (const v of values) search.append(key, String(v));
	values.forEach((v, i) => search.append(`${key}[${i}]`, String(v)));
	const qs = search.toString();
	return qs ? `${url}?${qs}` : url;
	};
	const withIndexedQuery = (url: string, key: string, values: Array<string | number>) => {
	const search = new URLSearchParams();
	values.forEach((v, i) => search.append(key + '[' + i + ']', String(v)));
	const qs = search.toString();
	return qs ? url + (url.includes('?') ? '&' : '?') + qs : url;
	};