fix: normalise event payload keys, implement updatePlayer, add pagination

[knytcomics-ui]

Summary

• Payload key normalisation — normalizePayload() added to the indexer converts all camelCase event keys to snake_case on ingest, so subscriptionExpiry, playerId, evidenceUri, unlockedAt, txHash, and metadataUri are all stored and read consistently as snake_case across the scout, validator, and player controllers
• PUT /api/players/:playerId implemented — accepts either a metadata object (pinned to IPFS) or a metadataUri directly, calls updateProfile() on the Soroban contract stub, and returns { transactionId, metadataUri } with HTTP 200 (previously returned a stub 202 with no data)
• Pagination for getEvents() — added limit/offset options and a getEventsCount() helper for paginated event queries
• src/services/store.ts removed — legacy in-memory store fully superseded by the SQLite-backed db layer

Closes #202

Test plan

• npm test — all 350 tests pass
• PUT /api/players/:playerId with { metadataUri: "Qm..." } returns 200 with transactionId and metadataUri
• PUT /api/players/:playerId with { metadata: { position: "GK" } } pins to IPFS and returns 200
• PUT /api/players/:playerId with neither field returns 400
• Scout subscription endpoint returns correct active/remainingDays using subscription_expiry key
• Scout contacts endpoint returns correct playerId and unlockedAt using player_id / unlocked_at keys
• Validator pending milestones endpoint filters correctly using player_id key