feat(viewer): add repository search filter

[amh1k]

Description

Adds a client-side repository search field to the Viewer landing page.

Users can filter the repositories table in real time using a case-insensitive substring match on repository names. The implementation uses inline vanilla JavaScript, requires no backend changes, and handles no-match and cleared-search states gracefully.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (describe below)

Manual testing in the Viewer confirmed:

• Search input is displayed above the repositories table.
• Matching repository names remain visible.
• Uppercase input matches lowercase repository names.
• A non-matching query hides all rows without browser errors.
• Clearing the search restores all rows.

Additional automated checks:

go test ./internal/viewer -run TestRenderTemplate_WithRepos
go test ./internal/viewer
make check

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

Closes #631

[github-actions]

✅ OpenCodeReview: No comments generated. Looks good to me.

[lizhengfeng101]

CI / test (pull_request)Failing after 10m

[amh1k]

CI / test (pull_request)Failing after 10m

I seem pretty lost on this. I verified the branch locally with make test, make check, the viewer race tests, and go vet. Could you please rerun the failed CI job?