feat: better error messages for incomplete/ambiguous target grammar

Summary

parseTarget errors are generic and unhelpful. When a user types dot tx Balances, the error says "Expected format: Pallet.Item" but doesn't suggest how to discover available calls.

Current Behavior

$ dot tx Balances
Error: Expected format: Pallet.Item

Expected Behavior

$ dot tx Balances
Error: Expected format: Pallet.call_name (e.g., Balances.transfer_allow_death)
  Hint: run "dot inspect Balances" to see available calls

$ dot tx Balancez.transfer
Error: Unknown pallet "Balancez". Did you mean "Balances"?
  Available pallets: Balances, System, Staking, ...

Proposed Changes

• src/utils/parse-target.ts: Add contextual hints to error messages (e.g., suggest dot inspect <Pallet> to discover items)
• src/commands/tx.ts: Enhance "Unknown pallet" errors with fuzzy suggestions from chain metadata
• src/commands/query.ts: Same fuzzy suggestion treatment for storage queries

Dependencies

• Depends on Issue tracking inspect listing calls (#79 or equivalent) — so the hint actually shows useful info.

Related Issues

• #46 (camelCase normalization) — related input handling improvement.

Priority

P2 — Polish after inspect shows calls. Quick win (size S).

Start with src/utils/parse-target.ts, then review src/commands/tx.ts and src/commands/query.ts for the existing target and unknown-pallet errors. Check Issue #79 or its equivalent first, since the inspect listing is a dependency for the suggested hint. Done means incomplete targets explain the grammar, unknown pallets offer fuzzy suggestions and available pallets, and storage queries receive the same treatment.