fix #459: use UTC for release year display

[SvenS7]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

This fixes a timezone-dependent release year display issue.

Root cause:

• Release year was derived using local timezone conversion from timestamps.
• In negative UTC offsets (e.g., America/New_York), 2026-01-01 00:00:00 UTC could display as 2025.

Changes:

• Use UTC conversion when deriving release year for display in artist and get all album date paths.
• Keep other timestamp displays (created_date, last played) unchanged.

Validation:

• Reproduced timezone difference with a small script.
• Ran Ruff on changed files:
  uv run ruff check src/swingmusic/api/artist.py src/swingmusic/api/getall/init.py
• Result: all checks passed.

Closes #459

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[Copilot]

Pull request overview

Fixes timezone-dependent off-by-one release year displays by ensuring the year is derived in UTC rather than the server’s local timezone, aligning UI output across negative UTC offsets (e.g., America/New_York).

Changes:

• Use timezone.utc when converting album/artist release timestamps to a display year.
• Remove an unused pprint import from the artist API module.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/swingmusic/api/getall/init.py	Derives the “date” sort help text year using UTC-based timestamp conversion.
src/swingmusic/api/artist.py	Derives an artist’s release year in UTC and removes an unused debug import.