Add retry limit to OAuth username generation loops

[Copilot]

The username generation loop in OAuth strategies (42, Facebook) had no upper bound, creating a potential infinite loop if all username variations were taken.

Changes:

• Add MAX_USERNAME_RETRIES = 10 constant at module level in both 42.ts and facebook.ts
• Return 500 error with clear message if unique username cannot be generated after max retries
• Update .gitignore to exclude TypeScript build artifacts (.d.ts, .d.ts.map, .js.map)

const MAX_USERNAME_RETRIES = 10;

// In callback handler:
let retryCount = 0;
while (isUsernameTaken) {
    if (retryCount >= MAX_USERNAME_RETRIES) {
        return reply.status(500).send({ error: 'Failed to generate unique username after maximum retries' });
    }
    // ... username generation logic
    retryCount++;
}

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