fix: code quality and safety improvements - #3340

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

Closing — this branch does not build. It contains changes I have already explained and closed twice (#3272/#3274 on 2026-07-29, #3279–#3300 on 2026-07-31):

• parseInt(searchParams.get("days", 10) ?? "90", 10) — URLSearchParams.get() takes one argument. This is a type error, and parseInt already had its radix in the correct position.
• .sort((a, b) => a - b) on arrays of strings — subtracting strings yields NaN, so the comparator is meaningless and sort order becomes unspecified.
• merged_at === null in place of == null — a regression: == null matches both null and undefined, and merged_at is optional here, so strict equality silently miscounts.

Type check and Build are red on this PR. Please run pnpm type-check locally before opening anything.