feat(scoring): add language-specific causes of death

[mvanhorn]

What changed

• Added 6 language-specific entries to the rules array in determineCauseOfDeath() (src/lib/scoring.ts) covering Ruby, Python, PHP, Perl, CoffeeScript, and Objective-C. The three "still-active but aging" languages (Ruby, Python, PHP) score 4 only when daysSince > 365; the three "historically fading" languages (Perl, CoffeeScript, Objective-C) score 5 since their decay signal is strong regardless.
• Added 3 unit tests in src/lib/scoring.test.ts verifying the new causes return for the matching language (Ruby Gemfile quip, Perl reader-incredulity quip, Objective-C Swift quip).

Why

• Closes Add language-specific causes of death to scoring #10. The existing code only had one language-scoped rule (JavaScript → "Lost in dependency hell"). The issue asked for at least four more, preferably accurate to each ecosystem rather than mean-spirited.
• The causes mirror the examples in the issue body (Gemfile.lock never unlocked, Pip froze, Died of PHP fatigue, Nobody could read it including the author, Outlived by the thing it inspired, Swift happened) so the maintainer's intent is preserved verbatim.
• Scores kept in the 4-5 range so they coexist with the existing distribution: isArchived (10), fix typo (8), fork (7), isJS (5). Aging languages don't drown out the stronger signals, but they do outrank the generic fallback "Side project syndrome" (score 1) when the repo has a matching language.

Checklist

• I tested my change locally (npm run lint and npm test) — both pass; 35/35 tests green including the 3 new ones.
• I kept the scope focused and avoided unrelated refactors — only the rules array and three new test blocks were touched.
• I updated docs/screenshots if behavior or UI changed — N/A (logic-only change).
• I confirmed no secrets are added.

Screenshots (if UI change)

N/A — scoring logic only, no UI surface touched.

Fixes #10

This contribution was developed with AI assistance (Codex).

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