feat: add account/close, billing/plan, payout-methods default, and wallet/pending endpoints

[HasToBeJames]

Description

Implements four missing routes-d endpoints: closing a user account with a reason, fetching subscription plan info, setting a payout method as default, and listing pending wallet balances.

Closes #1047
Closes #1046
Closes #1034
Closes #1027

Changes proposed

What were you told to do?

Implement the four routes-d endpoints listed above with auth, validation, structured errors, and unit tests.

What did I do?

POST /api/routes-d/account/close (#1047)

• Auth and ownership check via verifyAuthToken + prisma.user
• Returns 409 if account already closed
• Validates reason: optional string, max 500 chars, returns 422 on violation
• Updates user.status to 'closed', returns closedAt timestamp
• Tests: 401 (no token), 401 (invalid token), 401 (user not found), 409 (already closed), 200 (with reason), 200 (no reason), 422 (reason too long)

GET /api/routes-d/billing/plan (#1046)

• Auth check, loads user with subscription relation
• Falls back to 'free' plan when no subscription exists
• Returns plan key, displayName, monthlyPriceCents, features array, renewsAt, status
• Plan details table: free/starter/pro/enterprise
• Tests: 401 (no token), 401 (invalid), 401 (no user), 200 (free fallback), 200 (pro), 200 (enterprise -1 price)

PATCH /api/routes-d/payout-methods/[id]/default (#1034)

• Auth + ownership check (method must belong to authenticated user)
• Returns 404 if method not found for user
• Returns 409 if method already default
• Uses to atomically unset old default and set new one
• Tests: 401, 401 (user not found), 404, 409 (already default), 200 (sets new default)

GET /api/routes-d/wallet/pending (#1027)

• Auth check, returns all pending transactions for user
• Aggregates totals grouped by currency
• Returns: pending[], totals{currency: amount}, count
• Tests: 401 (no token), 401 (invalid), 401 (no user), 200 (empty), 200 (multi-currency totals)

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the main branch (left side).
• My commit messages styles matches our requested structure.
• The implementation was reviewed and confirmed to work as intended.
• I am only making changes to files I was requested to.

Screenshots / Validation Evidence

8 files added: 4 route handlers and 4 test files. Auth pattern, error envelopes, and Prisma mock structure match existing routes-d conventions.

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