NFT gallery (Soroban CAP-46)

[attyolu]

##closes #349

## Summary

Closes #349. Implements the `/nfts` gallery route in `frontend/wallet` to detect, filter, and render Soroban CAP-46 non-fungible tokens held by the connected wallet.

## Key Changes

### 1. NFT Gating & Correctness Rules (`frontend/wallet/lib/nfts.ts`)
- **Fixture Gating**: Fixture NFTs are strictly gated behind an explicit opt-in (`NEXT_PUBLIC_NFT_FIXTURES=1` or `includeFixtures: true`). They are **never** rendered in production or used as a fallback for empty results or network errors.
- **Owner Preservation**: Item owner addresses are never mutated or rewritten to the connected wallet address.
- **Indexer Endpoint**: Configured `NEXT_PUBLIC_WRAITH_URL` (or `NEXT_PUBLIC_INDEXER_URL`) as the base URL, defaulting to `https://wraith-0jo1.onrender.com`.

### 2. Gallery UI & Distinct States (`frontend/wallet/app/nfts/page.tsx`)
- **Real CAP-46 Render**: Displays real on-chain CAP-46 NFTs held by the wallet.
- **Empty State**: Renders a dedicated empty state banner when the wallet holds 0 CAP-46 tokens.
- **Distinct Error State**: Renders an error card displaying failure details and a working **Retry Fetching** button when indexer API requests fail.
- **Dev Controls**: Added quick test toggles for verifying empty and error UI states.

### 3. Environment Variables & Documentation (`.env.example`)
- Documented `NEXT_PUBLIC_WRAITH_URL` and `NEXT_PUBLIC_NFT_FIXTURES` in `frontend/wallet/.env.example` and root `.env.example`.

### 4. Unit Test Suite (`frontend/wallet/lib/__tests__/nfts.test.ts`)
- Added tests for fixture gating, error throwing on fetch failure, owner non-mutation, CAP-46 transfer filtering, and empty state returns.

---

## Acceptance Criteria Verification

- [x] **Renders real CAP-46 NFTs held by the connected wallet**: Queries Wraith indexer `/transfers/address/:address` and filters CAP-46 contracts.
- [x] **Fixture NFTs gated**: Gated behind `NEXT_PUBLIC_NFT_FIXTURES=1` / `includeFixtures: true`. Never rendered as a fallback.
- [x] **Wallet holds no NFTs → real empty state**: Returns `[]` and displays empty state UI.
- [x] **Fetch fails → distinct error state with retry**: Throws error on HTTP failure and renders distinct error card with Retry button.
- [x] **Indexer base URL comes from env var**: Configured `NEXT_PUBLIC_WRAITH_URL`, documented in `.env.example`.
- [x] **No fabricated holdings / owner rewriting**: Owner property preserved as true on-chain owner or fixture owner.

---

## Test Plan

Run Jest unit tests in `frontend/wallet`:
```bash
npm test frontend/wallet/lib/__tests__/nfts.test.ts

PASS lib/__tests__/nfts.test.ts
  Soroban CAP-46 NFT Module
    FIXTURE_NFTS
      ✓ contains at least one fixture NFT (2 ms)
      ✓ each fixture has required CAP-46 fields (name, image, attributes, standard) (2 ms)
    truncateAddress
      ✓ truncates a long Soroban contract address correctly
      ✓ returns short addresses unchanged (1 ms)
    formatTokenId
      ✓ formats numeric token IDs with leading hash
      ✓ handles string token IDs correctly
    fetchWalletNFTs
      ✓ throws error when indexer fetch fails and fixtures are not enabled (10 ms)
      ✓ returns fixture NFTs when includeFixtures is explicitly true
      ✓ never overwrites fixture owner with connected wallet address
      ✓ filters CAP-46 transfers when Wraith responds with token transfers
      ✓ returns empty list if includeFixtures is false and no on-chain NFTs exist (Empty State test) (1 ms)

Test Suites: 1 passed, 1 total
Tests:       11 passed, 11 total

## Summary
<!-- What does this PR change and why? -->

## Related issue
<!-- Closes #123 -->

## Type of change
- [ ] Bug fix
- [ ] New feature
- [ ] Refactor
- [ ] Docs
- [ ] Tests
- [ ] CI / tooling

## Component
- [ ] Wallet frontend
- [ ] SDK
- [ ] Contracts
- [ ] Agent

## Checklist
- [ ] I have read [CONTRIBUTING.md](../CONTRIBUTING.md)
- [ ] `cargo test` passes (contracts)
- [ ] `npm run typecheck` passes (wallet / sdk / agent)
- [ ] `npm run build` passes (wallet / agent)
- [ ] I added or updated tests where relevant
- [ ] I updated docs / README where relevant

## Screenshots / test output
<!-- For UI changes, include before/after screenshots. For tx flows, include tx hashes. -->

[vercel]

Someone is attempting to deploy a commit to the miracle656's projects Team on Vercel.

A member of the Team first needs to authorize it.

[attyolu]

Thanks for the review. I’ve fixed the in-repo code issues that were causing the mobile typecheck and wallet build failures:

removed the duplicate merge-conflict style blocks in the mobile app
cleaned up the duplicate style declaration / theme token issue in the mobile landing screen
I also verified the relevant checks locally:

mobile typecheck passes
wallet production build passes
NFT regression tests pass
The remaining GitHub checks are external to the code fix:

the Vercel checks are failing because the project has not been authorized for deployment in GitHub, so those jobs cannot complete until repo/Vercel access is granted
the Playwright wallet E2E check is a CI environment check and still needs to be re-run in the GitHub Actions environment with the required browser setup/secrets
In other words, the code-level issues in this branch have been resolved, and the remaining red checks are authorization/environment blockers rather than repository compile failures.