[BUG]: computeHealthScore & computeActivityClassification give wrong output for missing/null pushed_at

[RounakKumarAgarwal]

Bug Description

computeHealthScore() and computeActivityClassification() in src/services/analytics.js
parse repo.pushed_at with an unguarded new Date(repo.pushed_at). GitHub can return
pushed_at as null or omit it (e.g. a newly created or empty repository), and in those
cases both functions produce incorrect output with no error:

• pushed_at missing (undefined) -> computeHealthScore returns NaN, which renders in the
  UI and corrupts any sorting/averaging that consumes the score.
• pushed_at: null -> new Date(null) resolves to the Unix epoch (1970), so
  computeHealthScore returns a plausible-looking but wrong value and
  computeActivityClassification labels the repo "Hibernating" — a confidently incorrect
  classification for what may be a brand-new repo.

getTopRepositories() in the same file already guards this exact case:
Number.isFinite(pushedAtMs) ? ... : Infinity. The guard just wasn't applied to the two
functions above, so the codebase is internally inconsistent about handling the same field.

Steps to Reproduce

1. Open src/services/analytics.js.
2. Call the functions with a repo that has no valid pushed_at, e.g. in a node REPL:

import { computeHealthScore, computeActivityClassification } from './src/services/analytics.js'

computeHealthScore({ open_issues_count: 2 }, 1)                   // -> NaN
computeHealthScore({ pushed_at: null, open_issues_count: 0 }, 3)  // -> 39 (misleading)
computeActivityClassification({ pushed_at: null })               // -> "Hibernating" (wrong)

3. Observe: no error is thrown; the NaN / epoch-derived values flow into the analytics model and the UI.

Logs and Screenshots

Reproduced locally on main (Node v22.17.0):

computeHealthScore({ pushed_at: null }):            39           (plausible but wrong)
computeActivityClassification({ pushed_at: null }): Hibernating  (wrong label)
computeHealthScore({ pushed_at: undefined }):       NaN

Environment Details

• OS: Windows (MINGW64 / Git Bash)
• Browser: Chrome
• Node.js: 22.17.0
• Branch: main
• Affected functions: computeHealthScore, computeActivityClassification (src/services/analytics.js)
• Existing tests in src/services/analytics.healthMetrics.test.js only feed valid dates,
  so this path is currently uncovered.

Impact

Medium - Feature works but has issues

Code of Conduct

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates

[notstanzinn]

Hi @RounakKumarAgarwal , I'd like to work on this issue. I plan to fix the handling of missing/null pushed_at values in computeHealthScore and computeActivityClassification, and add regression tests for these cases. Could you please assign this issue to me?

[RounakKumarAgarwal]

I'm already working on it and waiting for the maintainers response so that i can create a PR, so please look for other issues to contribute . @notstanzinn