lint: resolve pre-existing Ruff violations in scripts/, tests/, and pythonlings/

[Huoyanlifusu]

Problem

With the Ruff checks added in #127 (advisory for now), the non-curriculum code reports 176 pre-existing violations:

Scope	Count
scripts/	38
tests/ (integration, unit, tui)	77
pythonlings/ (core, cli, screens, widgets)	61

Breakdown: 164 × E501 (line too long), 10 × I001 (unsorted imports), 2 × F401 (unused imports) — 12 auto-fixable. All reported by:

ruff check scripts tests pythonlings --ignore F821

These stay unfixed today, so when #124 flips lint from advisory to blocking, CI goes red immediately.

Proposed Behavior

• Run ruff check scripts tests pythonlings --fix + ruff format for the auto-fixable subset.
• Hand-fix the rest (long strings/comments that format can't touch).
• Land as one or two focused PRs targeting dev (e.g. one for tests/, one for scripts/ + pythonlings/), each keeping CI green and tests passing (python -m pytest -q).
• Acceptance: the command above reports 0 errors.
• checks/ (curriculum) stays out of scope — separate discussion.

Alternatives Considered

• Fix repo-wide including checks/: touches learner-facing teaching files and bloats diffs; the curriculum needs its own maintainer decision.
• Split by rule type: same files hit by multiple rules would scatter the work across PRs and cause conflicts.
• Leave as-is: fine while lint is advisory, but blocks ci: add automated style linting (ruff) so style issues are caught before review #124's end goal.