fix(api): handle nulls in ranking query and log error stack trace (closes #84)

[trexfr-ops]

Description

Closes #84

This PR resolves the 500 error on the /ranking endpoint when executed against a clean database and ensures full error logging.

Key Changes

1. Added full server-side stack trace logging with console.error("Error in GET /ranking handler:", error) in api/src/server.ts so any future internal handler failures are captured in the server log.
2. Wrapped ciudadanos_matados and criminales_matados in COALESCE to guarantee safe arithmetic on nullable stats in api/src/repositories/characters.ts.
3. Handled empty database queries cleanly returning status 200 with { characters: [] }.

/claim #84

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Summary by Gitar

• Database Schema & Migrations:
  • Moved clan_members table definition before data migrations in api/schema.sql
  • Wrapped database migration script in an atomic transaction with rollback support in api/src/migrate.ts

_{This will update automatically on new commits.}

[gitar-bot]

Code Review ✅ Approved

Refactors ranking query null handling and database migration scripts to resolve 500 errors on clean databases, while adding full error stack trace logging. No issues found.

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