FOLLOW-UP 4.1: Batch all poll RPC calls into a single JSON-RPC batch

The current poll fires ~19 individual HTTP POST requests per cycle (1 eth_getBlockByNumber latest + 1-2 eth_getLogs + N eth_getBlockByNumber for swap timestamps + N eth_call for slot0/liquidity). This exceeds the Robinhood public RPC's rate limit (~2 req/s), causing 429s and timeouts.

FIX: Collect all RPC calls needed for one poll cycle and send them as a SINGLE JSON-RPC batch (one HTTP POST with an array of request objects). Parse the array response. This is 1 HTTP request instead of 19.

1. BATCH MECHANISM:

   • JSON-RPC 2.0 batch: POST a JSON array: [{"jsonrpc":"2.0","id":1,"method":"eth_getBlockByNumber","params":["latest",false]}, {"jsonrpc":"2.0","id":2,"method":"eth_getLogs","params":[...]}, ...]
   • Response is a JSON array of results in the same order (matched by "id")
   • If the RPC returns a single object instead of an array (some nodes don't support batch), fall back to sequential calls with 500ms gap
   • If the RPC returns an error for the batch (e.g. "batching not supported"), fall back to sequential with 500ms gap
   • The Robinhood public RPC (rpc.mainnet.chain.robinhood.com) supports JSON-RPC batch (confirmed: it answers multi-method arrays)

2. POLL CYCLE RESTRUCTURE:

   • Phase 1 (1 batch): eth_getBlockByNumber("latest", false) + eth_getLogs (V4) + eth_getLogs (V3, if enabled)
   • Parse response. Determine which pools are active.
   • Phase 2 (1 batch): For each active pool, eth_getBlockByNumber(swapBlock, false) + eth_call (slot0 or liquidity)
   • Total: 2 HTTP POSTs per poll cycle instead of 19
   • If Phase 1 fails, retry after 60s (existing behavior)
   • If Phase 2 has individual call errors, mark those pools UNKNOWN (existing behavior)

3. RPC CLIENT CHANGE:

   • Add a batchRequest(calls) method to createRpcClient that takes an array of {method, params} objects
   • Assigns sequential ids, POSTs the array, parses the array response
   • Returns an array of results (or {error} for individual failures)
   • Keep the existing single-request method for quotes and other non-poll calls
   • Timeout: 30 seconds for the batch (generous, since it's one request)

4. WORKER (if still using the proxy):

   • The Worker just passes through whatever the browser sends. No changes needed to the Worker logic.
   • The 500ms gap in the Worker can be removed (or set to 0) since there are now only 2 requests per poll instead of 19.
   • Keep the retry-on-429 logic as a safety net.

5. KEEP UNCHANGED:

   • All monitor logic (window, staleness, slot0, pool status, spreads, auto-mode)
   • Quote mechanism (still individual eth_call, not batched)
   • V4 and V3 execution paths
   • UI, wallet transfer, activity log
   • 30s poll cadence, 60s error retry
   • All existing tests (update call-count assertions to expect 2 HTTP requests per poll instead of 19)

6. VERIFICATION:

   • The batch response must be tested: correct id matching, partial failures (one call in the batch reverts, others succeed), empty logs array, all-pools-inactive case
   • Fallback path (sequential with 500ms gap) must be tested for RPCs that don't support batching
   • Live read-only: run one poll cycle against rpc.mainnet.chain.robinhood.com and confirm 2 HTTP requests total, correct pool data

DELIVERABLE: Updated index.html + js/v4-arb-encoder.js. Same repo.