Add Swedish (sv) translation

[dchaudhari7177]

Closes #1.

Adds Swedish to claude_usage/i18n.py.

What changed

• "sv": "Svenska" added to LANG_NAMES, so it shows up under right-click → Language using the language's own name.
• A "sv" entry for all 148 STRINGS keys — nothing falls back to English.

Only additions: 149 inserted lines, 0 deletions. No existing translation or formatting was touched.

Translation notes

• Placeholders — every {} is preserved, in the same order and count as the English string. I checked this programmatically across all 148 keys rather than by eye.
• Panel strings are deliberately short, since the panel is small: 5 T / VECKA for the short labels, VECKOGRÄNS for the weekly limit, 5-TIMMARSFÖNSTER for the 5-hour window. The longer prose is confined to the settings and sign-in dialogs, where there is room.
• Swedish spacing convention — a space before the percent sign ({} %/tim), which is standard Swedish typography and matches how the existing European locales handle their own conventions.
• Windows terminology — aktivitetsfältet (taskbar), Startmenyn (Start menu), Starta med Windows (start with Windows), to match what Swedish Windows 11 itself calls these.

How I tested

python -c "import claude_usage.i18n as i;
i.set_language('sv');
print(i.tr('panel.updated','12:30'), i.tr('hist.stat_forecast'))"

• The module imports and STRINGS parses.
• Asserted 'sv' in LANG_NAMES, and that 0 of 148 keys are missing an sv entry.
• Asserted the {} count matches English for every key — 0 mismatches.

I do not have a Windows 11 desktop session to run the PySide6 panel in, so I have not visually confirmed overflow in the live panel. I kept the panel labels at or below the length of the existing German/Dutch strings, which are the longest currently shipping, so they should not be the ones that overflow first — but please do give it a look on your machine.

Note on the sibling issues

I have also opened PRs for #2 (Japanese) and #3 (Chinese). They each touch the same 148 blocks in i18n.py, so whichever merges first will leave the others needing a trivial rebase. Happy to rebase mine as soon as you merge any one of them — just say the word.