fix: add rate limiting to /auth/login and /auth/register

[RudraDudhat2509]

Fixes #260

What changed

/auth/login had zero rate limiting — only /auth/forgot-password had a limiter. Combined with predictable @iitbhilai.ac.in usernames, this left the login endpoint open to unlimited automated password guessing.

Added the same express-rate-limit pattern already used for forgot-password — 10 requests per 15 minutes — to both /auth/login and /auth/register.

Testing

This PR was cut before #266 merged, so it re-adds the same backend test setup (jest + supertest + mongodb-memory-server) — no conflict, just means both PRs happen to touch package.json the same way; whichever merges first, the other will just no-op that part.

Test fires 11 login attempts with bad credentials against a live (in-memory) Mongo instance and asserts the limiter kicks in before all 11 go through.

Verified the test is meaningful — ran it against the old unprotected route first:

BEFORE (old code): 0 requests blocked — test fails, none of the 11 attempts get throttled
AFTER  (this fix):  request blocked with 429 once the limit is hit — test passes

Run with npm test in backend/.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3a38811 and cd284fb.

⛔ Files ignored due to path filters (1)

• backend/package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (3)

• backend/package.json
• backend/routes/auth.js
• backend/tests/authRoutes.loginRateLimit.test.js

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