fix(frontend): replace Findings API response any with typed contract

[SathvikaSingoti]

Description

The Findings page cast the getFindings API response to any in its initial fetch and loadMore callbacks, which hid pagination/result shape mistakes from the type checker. getFindings already returns a typed FindingsResponse (with findings?: FindingRecord[]) in api.ts, so this PR traces that type through the Findings page instead of discarding it.

Related Issues

Closes #1401

Type of Change

• Refactor / type safety (non-breaking, no behavior change)

How Has This Been Tested?

• Replaced (data: any) with (data: FindingsResponse) in the initial fetch effect and removed the any-adjacent as Finding[] blind cast in loadMore.
• FindingRecord.id is string | undefined (shared type used across many endpoints), while the page's local Finding type requires id: string. Rather than weakening either type, both fetch paths now filter out any finding missing a valid id before assigning state, since a finding without an id can't be selected, checked, or reviewed anyway. This is stricter/safer than the previous blind cast.
• Ran npm run typecheck - passes with no errors.
• Ran npm run test - 537/537 tests passing across 61 files.
• Ran npm run build - builds clean.
• Ran bash scripts/check-artifacts.sh origin/main - no tracked generated artifacts or cache files in the diff.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.