refactor: remove any usages and improve type safety in public routes

[pari7maheshwari]

Summary

Closes #553

Removes all any usages from apps/backend/src/routes/public.ts by introducing proper TypeScript types for query parameters and card link response mapping. No runtime behaviour is changed.

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Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• UI / Design change
• Tests only
• Documentation
• Infrastructure / DevOps
• Security

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What Changed

• Added QrQuerystring interface ({ format?: 'png' | 'svg'; size?: string }) and typed the QR route's FastifyRequest with Querystring: QrQuerystring, replacing two (request.query as any) casts with direct request.query.format and request.query.size access
• Added CardLinkWithPlatform type via Prisma.CardLinkGetPayload<{ include: { platformLink: true } }>, replacing (cl: any) in the /card/:cardId response mapping with a proper generated Prisma type
• Added import type { Prisma } from '@prisma/client' to support the payload type — reuses the existing generated client, no new dependencies

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How to Test

1. Run npm run typecheck --workspaces --if-present — should pass with no new errors
2. Run npm run lint — should pass
3. Hit GET /api/u/:username/qr?format=svg&size=300 and GET /api/public/card/:cardId manually or via existing tests to confirm responses are unchanged

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Checklist

• My code follows the project's coding style (npm run lint passes)
• TypeScript compiles without errors (npm run typecheck --workspaces --if-present)
• I have added or updated tests for the changes I made
• All tests pass locally (npm run test --workspaces --if-present)
• No new console.log or debug statements left in the code
• Breaking changes are documented in this PR description

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Screenshots / Recordings

Not applicable — refactor only, no UI or API contract changes.

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Note for reviewers: Two pre-existing TypeScript errors (rateLimit does not exist in type FastifyContextConfig, lines 40 and 152) are visible in the Problems panel but were present before this PR and are out of scope for this issue.

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[github-actions]

Hi @pari7maheshwari,

Thanks for opening this pull request.

This PR has been automatically classified based on the files modified.

Applied Labels

• gssoc:approved
• backend

Primary Review Area

• backend

Reviewer

@Harxhit has been identified as the primary reviewer for this pull request.

If you have any questions regarding the affected area or implementation details, feel free to reach out to the assigned reviewer.

Thank you for your contribution!

[github-actions]

CI — All Checks Passed

Backend — PASS

Check	Result
Lint	PASS
Test	PASS
Typecheck	PASS

Mobile — SKIP

Check	Result
Lint	-
Test	-

Web — SKIP

Check	Result
Build	-

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Last updated: Tue, 30 Jun 2026 19:55:35 GMT

[Harxhit]

LGTM. Approving

[github-actions]

Congratulations @pari7maheshwari on getting PR #653 merged!

Thank you for your contribution to the project.

To receive the appropriate GSSoC labels and recognition, please mention @Harxhit in the #get-labels channel on our Discord server and share your merged PR link.