feat(api): add user earnings ledger

[lukevio]

What

Adds authenticated GET /users/me/earnings for #454.

Why

Players need an in-app payout ledger so they can audit pending and settled USDC earnings with Stellar transaction references.

How

• Adds /users/me/earnings protected by authenticate and requireActiveUser.
• Scopes payout records to the authenticated user.
• Supports status=pending|settled|failed|all with all as the default.
• Implements cursor pagination using created_at + id, with default limit=25 and max 100.
• Normalizes payout statuses into ledger statuses: pending, settled, or failed.
• Returns stellar_tx_hash: null for records without a submitted transaction hash.
• Adds totals for lifetime_earned_usdc and pending_usdc.
• Adds focused route tests for status filtering, cursor pagination, normalized response shape, and totals aggregation.

Test plan

• ./node_modules/.bin/vitest run apps/api/src/routes/users.earnings.test.ts
• ./node_modules/.bin/prettier --check apps/api/src/routes/users.ts apps/api/src/routes/users.earnings.test.ts
• git diff --cached --no-color | node scripts/gitleaks.mjs detect --pipe --redact --config .gitleaks.toml --verbose
• ./node_modules/.bin/tsc -p apps/api/tsconfig.json --noEmit currently blocked by existing unrelated apps/api/src/routes/leaderboard.ts(196,1): error TS1128.

Note: the local Husky hook invokes pnpm gitleaks:pre-commit, but pnpm exits first due ignored build-script approvals for @fingerprintjs/fingerprintjs-pro-react and @sentry/cli. I ran the underlying staged-diff gitleaks command directly and it passed.

Closes #454