feat(juicer): /v1/campaigns/juicer/progress + /spend endpoints

[joshuakrueger-dfx]

Summary

Backend for the Juicer NFT post-launch loyalty drop. Wallets trade `JUICER_JP_COST = 5000` Juice Points for a backend signature, then mint with that signature on Citrea Mainnet.

Endpoints

```http
GET /v1/campaigns/juicer/progress?walletAddress={addr}&chainId={4114|5115}
POST /v1/campaigns/juicer/spend { walletAddress, chainId }
```

`/progress` returns:

```json
{
"walletAddress": "0x...",
"chainId": 4114,
"availableJp": 5230,
"totalEarnedJp": 5230,
"spentJp": 0,
"cost": 5000,
"isEligibleForNFT": true,
"nftMinted": false
}
```

`/spend` is idempotent: a retried POST returns the stored signature instead of issuing a new one or deducting JP twice. Signatures are deterministic from `(contract, chainId, wallet)` so re-issuance is safe.

Source of truth

• `totalEarnedJp` ← `GET https://ponder.juiceswap.com/points/{addr}\` (depends on fix(points): unblock /points endpoints (500 -> data) ponder#138).
• `spentJp` ← new `juicer_spend` table (one row per wallet+chain, unique constraint).
• `nftMinted` ← best-effort on-chain `hasClaimed`; the contract's mapping is the second line of defence against double-claim.

Fail-closed properties

• `/spend` returns 503 if `JUICER_NFT_CONTRACT` env var is empty (contract not deployed yet) — the frontend renders a "not yet live" state instead of minting against a placeholder.
• `/spend` returns 503 if ponder `/points` is unreachable — never silently lets a wallet spend against a stale balance.
• The unique `(walletAddress, chainId)` constraint plus the contract's `hasClaimed` mapping form a defence-in-depth pair against double-claim and race conditions.

DB migration

`prisma/schema.prisma` adds the `JuicerSpend` model. Apply with `yarn prisma migrate dev --name juicer_spend` before deploying.

Env vars

```bash
JUICER_NFT_CONTRACT=0x... # populate after smart-contracts#56 deploys
CAMPAIGN_SIGNER_PRIVATE_KEY=0x... # already used by First Squeezer; reuse
CITREA_4114_RPC_URL=https://... # already set
```

Companion PRs (hard dependencies)

• fix(points): unblock /points endpoints (500 -> data) ponder#138 — `/points` endpoint must return real data
• feat(nft): JuicerNFT loyalty drop contract + tests smart-contracts#56 — `JuicerNFT.sol` deploy + populate `JUICER_NFT_CONTRACT`
• feat(juicer): Juicer NFT page (5,000 JP + X follow + Discord) bapp#741 — frontend consumer of these endpoints

Test plan

• DB migration applied
• Set `JUICER_NFT_CONTRACT` env var to deployed address
• `GET /v1/campaigns/juicer/progress` for an unconnected address returns `availableJp: 0, isEligibleForNFT: false`
• `GET /v1/campaigns/juicer/progress` for a wallet with >=5000 JP returns `isEligibleForNFT: true`
• `POST /v1/campaigns/juicer/spend` for a wallet with <5000 JP returns 403
• First successful `POST /spend` returns 201 with signature; second returns 200 with the same signature (idempotency)
• On-chain `JuicerNFT.claim(signature)` succeeds and contract emits `NFTClaimed`