fix: resolve all pre-existing backend eslint errors and add eslint config

[Rudra-clrscr]

Adds backend/eslint.config.js (none existed before) and fixes every error it surfaces except middleware/fileValidation.js (separately tracked, in progress). Several of these were one-off typos or single duplicate lines; a few turned out to be much larger merge-corruption issues.

Small fixes:

• config/index.js: configs.development -> config.development typo.
• utils/emailRules.js: matchingRule.type -> matchedType (the actual variable holding the matched rule's type in that scope).
• utils/fileValidation.js: drop an unnecessary regex escape.
• utils/utils/emailTransporter.js -> utils/emailTransporter.js: fix a duplicated-directory path bug (authController.js requires '../utils/emailTransporter', which never existed at that path).
• server.js: fix an empty catch block (log the error instead of silently swallowing it) and remove a require for './routes/visualRoutes', a file that never existed anywhere in the repo (dead "VBSF routes" stub, not implemented on the Node side).

Larger fixes (duplicate/corrupted code from bad merges):

• middleware/adversarialGuard.js: removed a duplicated detectAdversarialPatterns call, a duplicated adversarialGuard function stub, a duplicated outer if in monitorConfidence, and two catch clauses attached to the same try - all leftover copies with a working original alongside them.
• server.js: removed a broken, never-closed logStartupTime stub and its duplicated EvoMail/startup-timer requires that preceded the real, complete versions; moved the EvoMail/visual route app.use() calls to after const app = express() is defined (they previously ran before app existed, which would throw at runtime once the file parsed).
• routes/authRoutes.js: this file had ~11 controller functions (register, login, logout, getMe, googleLogin, updateAvatar, forgotPassword, resetPassword, changePassword, updateWebhook, getSessionStatus) each duplicated 2-3x (verified byte-identical copies), plus assignRole/getUserPermissions/getRolesAndPermissions whose bodies were corrupted/incomplete in every copy. More importantly, despite creating an Express Router, the file never once called router.get/post() - it only exported bare handler functions - while server.js did app.use("/api/v1/auth", authRoutes), passing a plain object where Express requires a router/middleware function. The whole auth API was not actually routed. Rewrote the file as a thin router that imports the (already complete, working) handlers from controllers/authController.js and wires each one to its documented @route (recovered from the file's own JSDoc comments) with the appropriate validator/rate-limiter/protect middleware, then exports the router. Deleted routes/prediction.route.js, an orphaned, never- required duplicate of predictionRoutes.js's /stats route that referenced a Prediction model that doesn't exist anywhere in the codebase; fixed predictionRoutes.js's own /stats route (same bug) to use the History model it already imports.

Verified: node --check on every touched file, npx eslint . (1 remaining error is middleware/fileValidation.js, tracked separately), a full server.js boot with dummy env vars (previously impossible - it couldn't get past its first require), and the existing Jest (16/16) and node:test (26/26) suites still pass.

Left as pre-existing, separately-tracked issues (not touched here):

• middleware/fileValidation.js's own parsing error (your in-progress work).
• services/otpService.js exports rate limiters instead of OTP functions - unrelated corruption discovered while tracing authRoutes.js's dead requestOTP/verifyOTP/getOTPStatus imports (no working implementation of those three exists anywhere, so they were dropped from the new router rather than inventing the feature).
• 63 remaining eslint warnings (mostly unused vars/imports across many files) left non-blocking, consistent with the frontend cleanup PR.

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[Rudra-clrscr]

@Userunknown84 this is an extra PR needed for solving CI issue

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Pull request overview

This PR introduces a backend ESLint flat config and fixes a large set of pre-existing backend issues surfaced by linting and merge corruption, including making auth routing functional and removing dead/broken server code.

Changes:

• Add backend/eslint.config.js, add a backend lint script, and introduce ESLint dependencies.
• Repair backend runtime wiring issues (auth router export/wiring, server startup ordering, dead route removal).
• Fix correctness issues in prediction stats and various utility/middleware cleanups.

Reviewed changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
backend/utils/fileValidation.js	Regex cleanup for CSV formula-injection guard.
backend/utils/emailTransporter.js	Adds a centralized Nodemailer transporter module.
backend/utils/emailRules.js	Fixes rule-applied field to use the matched rule type variable.
backend/server.js	Removes broken/duplicated startup stubs, fixes route registration order, improves error logging.
backend/routes/predictionRoutes.js	Fixes /stats to use History model fields; minor handler restructuring.
backend/routes/prediction.route.js	Deletes an orphaned duplicate stats route file.
backend/routes/authRoutes.js	Replaces corrupted/duplicated handlers with a proper Express router wiring controllers + middleware.
backend/package.json	Adds lint script and ESLint-related devDependencies.
backend/package-lock.json	Locks ESLint-related dependencies.
backend/middleware/adversarialGuard.js	Removes duplicated/corrupted code and replaces an empty catch.
backend/eslint.config.js	Adds ESLint flat config for backend.
backend/config/index.js	Fixes fallback config typo (configs.development → config.development).

Files not reviewed (1)

• backend/package-lock.json: Generated file

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