Replace starter GraphQL schema with SO4 protocol entities

[0xsteins]

Summary

closes #182

Replaces the starter SubQuery schema (generic accounts, payments, credits,
debits, transfers) with SO4 protocol entities modelling markets, pools,
orders, positions, fees, referrals, and protocol events, and aligns the
indexer mappings with the new transfer entity.

Closes #<ISSUE_NUMBER>

What changed

Schema (apps/s03-indexer/schema.graphql)

• Market & token metadata: ProtocolContract, Token, Market,
  MarketConfigSnapshot.
• Liquidity lifecycle: Deposit, Withdrawal, PoolBalanceSnapshot,
  MarketTokenTransfer — covering create / execute / cancel.
• Trading lifecycle: Order (create / update / freeze / execute /
  cancel), Position, PositionChange (increase / decrease / close),
  Liquidation, AdlEvent.
• Fees & referrals: FeeClaim, UiFeeAccrual, FundingFeeClaim,
  ReferralCode, TraderReferral, ReferralOwnershipTransfer.
• Indexed account, market, key, status, ledger, timestamp, and
  transaction-hash fields for app filtering.
• Protocol-scale values (token amounts, prices, USD 1e30, shares, signed
  deltas) stored as String/BigInt to preserve precision — never
  downcast to JS numbers.
• Per-entity comments documenting which contract event feeds each entity
  (mkt_new, dep_*, wth_*, ord_*, pos_*, liq_*, adl_*, fee /
  referral events, token / faucet activity).
• Starter-only entities removed; token/transfer observability retained via
  MarketTokenTransfer.

Mappings (apps/s03-indexer/src/mappings/mappingHandlers.ts)

• handleEvent now writes MarketTokenTransfer from token / market-token
  transfer events, keeping amounts as decoded strings.
• Stores canonical case-sensitive Stellar StrKey addresses for
  from / to / account (no lowercasing) so app filters match real
  on-chain accounts.
• Emits the contract as its canonical C... StrKey so it lines up with the
  configured contract ids and the decoded addresses.
• Reads the guaranteed event txHash directly; transactionHash is now a
  required field on MarketTokenTransfer.

Verification

bun run --cwd apps/s03-indexer codegen
bun run --cwd apps/s03-indexer build

Generated src/types and project.yaml are gitignored per project
convention (regenerated via the bun scripts), so they are not committed.

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