feat: batch query support via stdin JSON

Parent Epic: #63

Summary

Allow agents to query multiple storage items in a single CLI invocation, reducing round-trips and connection overhead.

Usage

echo '[{"target":"System.Number"},{"target":"System.Account","keys":["5FHn..."]}]' | dot query --batch --output json

Output

JSON array of results matching input order:

[
  {"target":"System.Number","value":12345678},
  {"target":"System.Account","keys":["5FHn..."],"value":{"nonce":42,"data":{"free":"1000000000000"}}}
]

Implementation

• Add --batch flag to query command that reads JSON from stdin
• Parse each item, resolve against metadata, execute queries
• Share a single RPC connection across all queries
• Keep existing single-target positional syntax untouched

Files

• src/commands/query.ts — add --batch flag and stdin parsing

Verification

• Batch query 3 different storage items, verify all results returned
• Mix plain storage and map queries in one batch
• Verify error handling: one bad target shouldn't fail the whole batch

Start in src/commands/query.ts, reviewing the existing query command and its single-target positional syntax. Add the --batch stdin path, then verify three storage items, mixed plain and map queries, shared results in input order, and that one bad target does not fail the whole batch.